I have been having a problem with my buttercreams not taking color. I have been making swiss meringue buttercream and regular buttercream and neither one are accepting the color. I used wilton color gels.
They all stay a pastel color and are speckled. I can get the color more vibrant if I add water to my icing and mix it a lot...but it's still never as bold or accurate as I want.
This is a recent problem, only the last 4 or 5 times I've baked. I have checked with both of my mentors and they have no ideas.
I used to have the same problem until I changed from gel colours - I used Americolour but the brand doesn't matter. I now use liquid, oil based candy colours Chefmaster is the brand I use. I think because the colours are oil based they mix into the buttercream - which is essentially a fat, and the colour stays consistent. I have used Chefmaster in both SMBC and IMBC very successfully.
Do you use salt in your buttercream recipe? I had some issue then I read somewhere to be sure to dissolve your salt in the liquid used in your icing to ensure it dissolves. ( Just a thought.) Also, I have never had good luck with Wilton colors. Once they are opened, they dry out quickly and get tacky. I haven't had any issues with the Americolor gels and if I do have issues, Americolor has great customer service to answer your questions.
Have you tried adding the water based colors to the water based part of the smbc?maybe if you add the color before you add the fat it'll take the color better.