Breeding blue into a paint program is frowned upon by a lot of paint silkie breeders from what I've seen. Honestly though it's already mixed into a lot of paint programs on accident (along with a lot of other genetics that pop up and cause color problems).
The problem with blue is it can be really hard to tell it apart from black at times. The shade of blue can vary so much, a highly melanized blue can look black. Once you've accomplished the goal of getting rid of the red leakage in your paint program you can always work on weeding the blue out of your flock through test breeding if you'd like. As long as you are open and upfront with buyers if you sell chicks/culls/hatching eggs etc I don't think you'd run into many problems adding the blue in.
Good luck with your paint program. I breed them too and it's a tricky color to get right especially in the males! I've only been at it for a couple years so still an amateur with plenty to work out in my own program. Most of my foundation stock don't show any red leakage but I'm struggling with it in some of the offspring. I made the mistake of breeding some cockerels that looked clear of it only to find on their first (and in some cases second) adult molt some red showed up. Lesson learned about not breeding any young cockerels unless I want to risk the red leakage! You can't really help but risk it with the girls since they are good at hiding it.
