How do I make a seamless parallelogram tile?
This post explains how you could make a seamless tile in the shape of any parallelogram. You can use this method for creating seamless isometric or diamond tiles, and even triangular tiles (just cut the parallelogram along a diagonal).
Start with a base image larger than the parallelogram shape you want to create. In the steps below I indicated which programs I use to do the step, but of course you can use any program that can do the desired operations. I chose the second image so that it is easier to see what is happening with the texture.
And now you have a seamlessly tileable image: