Gray Clay is Actually Brown

Gray clay is also named "Cyan clay block"

No, I'm referring to a block that appears as "Gray Stained Clay"; cyan is something else.

Duplicate of MC-16210.

/me groans.
This doesn't have anything to do with cyan clay! There is a block called "Gray stained clay". When I place it, it appears brown. In my inventory, it appears gray. THIS IS NOT A CYAN BLOCK!!!!!

/me wonders if @unknown has ever colours IRL...

@unknown in MC-16210

Dark brown + gray = light brown

http://minecraft.gamepedia.com/Stained_Clay

It is available in the same 16 colors that wool can be dyed, although the shading of the color is less vibrant.

So I uploaded the pix. Now do you see that they're different?

thoses are 2 diffrent blocks, there is no diffrence in texture between 1.7.9 and 1.8

Again, there is no difference.
You're showing screenshots of two different worlds with probably different resource packs, look at the grass colour.
The one block is a light grey stained clay, the other is a grey stained clay.
Create a new world in 1.7.x , place the clay blocks, and open the very same world in 14w25b and show me the difference.

Yeah, different worlds, but i dont have resource packs installed and both are single player. Different grasses because different biomes.
But just for you, I took a screenshot of the 1.7.x world in 14w25b. It's exactly the same block, different texture. (To be precise, it's a 1.7.5 world originally, if that matters.)

I just created a world in 1.7.5, and placed down a block of Gray Stained Clay and a block of Light Gray Stained Clay. I then opened that world in 14w25b. The colors of the blocks did not change between the two versions. The block in your first screenshot is Light Gray, the block in the second is Gray.