The black outlines on my BCT's bleed into the white frosting and look sloppy. How do you all keep them looking so crisp and clean?

Usually when I do the FBCT I let the dark outline color dry before filling it in. You know like crusting over.
I'm not sure if this helps w/ the bleeding but I can only say I've had it happen once but I think it was more because the cake was out for 2 days on my counter and it was a little warm.

so far i havent had this problem. even with my bc melting on me.. knocks on wood

i have a batman in my freezer ill have to see if that came out tomorrow