Can anyone tell how to color the like this, triangles are 1 fill color but gradient together..

[Abdur5FF5]

[Kurt Gold]

Which version of Illustrator are you using?

Also, can you elaborate a bit? At least I'm not quite sure what you are going to do.

[Abdur5FF5]

latest version, you see the background image of triangles? I am able to make that pattern but am unsure how to color it like this? You see each triangle has a single fill color but when viewed collectively of many trainagle, it looks like a gradient. Basically how do I color the background triangles like that?

[ensel]

I´ll give it a try:
(Sorry for my possibly bad english... I still use the old Illustrator CC 22, so something could be different if you use a newer version.)

1. Start with two triangles and group them. Name the group "Left Top" (it helps to give the layers descriptive names).
Make sure the triangles already have the desired size, it can be annoying to resize everything later...
Each of the triangles should have a slightly different color.
The colors don´t really matter now, you can easily change them later.

2. Duplicate The group and name the new group "Left Top".
Move this group down- The exact position doesn´t matter, you will make precise adjustments later. Change the colors of the "Left Bottom" triangles.
The image should  somehow look like this:

3. Now double-click the Blend Tool (W) in the tools-palette. In the options dialog select "Specified Steps" ,"4" and "Align to page". Klick "OK".
The Blend Tool should still be selected and you will see that your mousecursor changed.
Do one mouseclick on one of the triangles of the "Left Top" group.
Then make one mouseclick on one of the triangles of the "Left Bottom" group.
Illustrator will apply the blend in 4 steps and the image should look like this somehow:

4. You will see that your layers in the layers-palette changed automatically. There should be a new group named "Blend" with a new Layer "Path" on top of the groups "Left Top" and "Left Bottom".
Rename the Layer "Blend" to "Blend Left".
Select ONE anchor-point of the new "path", move it around and see what happens...
Move the anchor-point until all the triangles are aligned well.

Zoom in and out to check that everything is aligned well, no white background between the triangels and so on.
Now the image should look like this somehow:  

5. Duplicate the Layergroup "Blend Left" with all its contents and rename it to "Blend Right".
Move "Blend Right" to the right. I would suggest to rename the sublayers accordingly.

6. Duplicate "Blend Right" again and name it "Blend All".
Make sure you see the sublayers of "Blend All" in the layers-palette and delete all of these sublayers but NOT the "path" layer.
Still in the layers-palette select "Blend Right" and move it inside "Blend All", right below the "Path"-layer.
Do the same with "Blend Left".
The Layers should look like this:

7. Now select one of the anchor points of the "Path"-Layer of "Blend All", move it and see what happens.
The path should become a horizontal lign to make your colored pattern look correct.

8. To make it look great you can adjust the colors of the triangles now. All blended-colors will immediately adapt to your new colors.

 

 

9. You can mask the pattern by drawing a rounded rectangle above the layer "Blend All". Select the rectangle and the layer "Blend All" and choose Object-> Clipping Mask
Here is the result:

Perhaps anybody can suggest a more elegant and flexible solution?