I am making caramel swiss meringue buttercream and want to know if I can colour this buttercream or will this alter the recipe? 

thanks for your help

Sue

Do you mean you want to add a brown colour to the caramel SMBC to make it look like chocolate? You should be okay to do that, but watch the amount of liquid going into your BC after adding the caramel. Make sure  you use a gel or powder colour. If you mean adding cocoa, that would be fine too, but it will give you a choc/caramel taste. 

AI want to make the Swiss buttercream green for a soccer field. I use paste colours, will this be ok?

So is your SMBC going to be a flavour? Or just plain? I thought you were talking about flavours, not colours in your original post.

ASorry I am talking about both colour and flavours

AOkay, well when I add caramel to SMBC it does go a light golden colour. What I would do, if you want it green, is to take a small amount out, add some colour to it and see if you're happy with the green you get with it. If you're not happy with it then you may need to do another batch that is not flavoured with caramel. Or you could try the Lorann oils to flavour it, but I've never used them so not sure on that sorry.