First, your history lesson.
It's not the "purple" that fades ... it's the red (red + blue = purple).
In the mid-70's, Red Dye #2 was removed from the market. Something about if you eat 8000 POUNDS of it a day, you MIGHT get cancer or something. It was very inconclusive, but it was removed anyway.
This dye was very stable, but when it was removed from the market, there was nothing that was a good substitute.
The reds on the market today are not stable and can fade when exposed to bright light or sunlight. I can't remember the last time I had any fading, though. I use CK brand coloring.
First, your history lesson.
It's not the "purple" that fades ... it's the red (red + blue = purple).
In the mid-70's, Red Dye #2 was removed from the market. Something about if you eat 8000 POUNDS of it a day, you MIGHT get cancer or something. It was very inconclusive, but it was removed anyway.
This dye was very stable, but when it was removed from the market, there was nothing that was a good substitute.
The reds on the market today are not stable and can fade when exposed to bright light or sunlight. I can't remember the last time I had any fading, though. I use CK brand coloring.
Hello indydebi,
Thank you for the lesson 
I didn't know that. the reds are not stable and will find CK brand.
How about if I use purple color to RI? Is it going to fade too?
Thank you Thank you Thank you.
How about if I use purple color to RI? Is it going to fade too?
If the red used to make that purple is not stable (well, as stable as reds can get today), then the red part of it might fade and you'll end up with just the blue.
I learned this REd DyE #2 story when I made my sister's wedding cake , 20+ years ago. Rainbow theme, so lots of multi colored BC flowers. My best friend, who also ran the cake supply shop, was on the way to the church, so I swung in real fast to show her the cake. She came out to the van and I saw my flowers had faded! She's the one that explained it to me.
However, at the wedding, everyone was SO impressed on how I got multi shaded roses (pink roses with red trim, blue roses with purple trim). They thought I was a GENIUS! (Gosh, maybe I should call them all and correct that? 
)
How about if I use purple color to RI? Is it going to fade too?
If the red used to make that purple is not stable (well, as stable as reds can get today), then the red part of it might fade and you'll end up with just the blue.
I learned this REd DyE #2 story when I made my sister's wedding cake , 20+ years ago. Rainbow theme, so lots of multi colored BC flowers. My best friend, who also ran the cake supply shop, was on the way to the church, so I swung in real fast to show her the cake. She came out to the van and I saw my flowers had faded! She's the one that explained it to me.
However, at the wedding, everyone was SO impressed on how I got multi shaded roses (pink roses with red trim, blue roses with purple trim). They thought I was a GENIUS! (Gosh, maybe I should call them all and correct that?
)
Another lesson for free (LOL).
I will make a wedding cake and the color is Purple 
What can I do? How can I tell the bride?
Actually I am middle of tasting now.
I have Americolor violet and buttercream in the refrigerator
so I added some coloring and let it sit under the blight light which is close to the window but it is cloudy today.
I will see how the color change it .
Thanks.
Correction: The brand of coloring I use is called "Cake Craft" .... sold in my local cake decorating supply store.
And again ... I haven't had any fading happen in years. When I did have fading, it was when the cake was exposed to direct sunlight (shining in thru the van windows, for example). I don't think regular light will do it. Sometimes flurescent (sp?) lighting will impact it. And if you make the icing ahead of time, maybe let it sit out overnight, it will either fade or "settle" into its shade ok. (I make BC red roses ahead of time and they hold up fine....I just leave 'em on the counter.)
Correction: The brand of coloring I use is called "Cake Craft" .... sold in my local cake decorating supply store.
And again ... I haven't had any fading happen in years. When I did have fading, it was when the cake was exposed to direct sunlight (shining in thru the van windows, for example). I don't think regular light will do it. Sometimes flurescent (sp?) lighting will impact it. And if you make the icing ahead of time, maybe let it sit out overnight, it will either fade or "settle" into its shade ok. (I make BC red roses ahead of time and they hold up fine....I just leave 'em on the counter.)
Hi indydebi,
Here is the result.
I made IMBC and Dream buttercream then took some frosting to make purple frosting. IMBC purple is much prettier than BC for me. it was smooth and shiny looking. I piped some letters on the white buttercream and IMBC then left both outside for one hour and the both were fine.
No bleeding or fading. It was only 78F and cloudy outside. I will keep them and test them out tomorrow for warmer weather.
Kake
I read somewhere that purple will turn blue unless you use a bit of milk in the icing - for what it's worth.
Interesting! I use milk in my icing and my reds don't fade (i.e. purples won't turn blue when the red fades out)! Hey! Learn something new on here everyday!!!! 
I made cupcakes last weekend. I used premade buttercream from my bulk store because I was short on time. I dyed it purple with americolor violet and accidentally left the cupcakes sitting near a window. It wasn't that sunny outside but within an hour my icing looked like blue and purple tye-dye.
I'm new to decorating and one of my first orders is a very dark purple high school color theme for bobcat pawprints and lettering. My cake instructor had advised us to always use water instead of milk when making icing, as buttercream can turn rather quickly if sitting out. So unfortunately, I did that. But I now have time to 'fix' the frosting with milk. I made FBCT pawprints and they turned out great, but when I peeled the wax off, the wax was stained pink and the purple pawprint was a lighter shade of purple. I thought the heat might fade the purple, but happy to hear it's the light that does it.
Thanks ladies!
Hi everyone
I too also made some cupcakes with a bright purple frosting for a bake sale. I made my butttercream with water as always and by the time they got to the function I no longer have bright purple I had blue I was like what the %&*%. Then when people started to buy and eat them they where like hey how did you do the get blue on the outside and purple on the inside. I was like that is my secret all along not knowing what was going on. I figured it out when I returned home and the few I left behind where still bright purple took 1 outside and within 30 minutes guess what it was blue too. Lesson learned I will not make anything purple that will be exposed to sun anymore. Have a good day
Kerri
CakeWhisperer - it is totally fine to use a bit of milk in your bc. the sugar stabalises it, so you dont need to worry about it going off. it sits out just fine too.
xx
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