If you mean by expressions, expressions aren't currently able to sample a layers pixel values.
But if you just want to use the solid as an 'optical filter' to tint the layers below, you could play around with 'blend modes'. Most notably 'color', or 'multiply'.
There are other ways of accessing a solid's color by applying a 'fill' effect and using the color of the fill effect to drive another expression.
But what is it you're trying to achieve?
Bar3nd
Raamw3rk - digital storytelling and visual effects