How much yellow gel food coloring should I add to yellow boxed cake mix to get a really yellow cake without it tasting bad?

When making the raspberry part of my lemon raspberry marble cake I found that the color bakes more intensely than the batter indicates. I don't add color to the lemon part because the color is perfect as is. I would add a tiny bit at a time until the batter is about 2 shades lighter than what you want it to look like once it's baked.

I'll try that. Thanks!