Changing vanilla textures based on a variable

I am currently trying to make a mod that makes weather have a greater effect on gameplay, along with a few other features including a temperature system. The problem I'm experiencing is with changing the color scheme of certain biomes during the seasons that the mod will add. For example, during spring, I want oak leaves to be pink, or during fall I want grass to be orange. How can I make a vanilla block change its color or texture depending on a variable?