Detectiing white portion in a textured plane

Hello, I have mapped texture onto a plane. Texture has got some while color. When my mouse touches that white portion, I would like to know that the color of that point is white. How can I do that? Thanks in advance.

You can use glReadPixels to read the pixel at the mouse location.

Actually I hv a plane and I am getting a point on the plane. How can I find the corresponding pixel of a point on a textured plane?