Advanced Graphics
Euphoria can be used to create a variety of graphic-intense programs in a variety of OS environments.
Search the Euphoria Code Archive for "graphics" and you'll find a plethora of libraries available for handling the graphics needs of your next program.
For GUI
If you're going to be doing GUI and graphics programming, it's best to make your attempt with a cross-platform library. You can be sure that 99% of your potential customers will have an OS that can run your software. If you use something that is only Linux specific, you leave out all the Windows customers, and vice versa.
For Graphics
Again, a cross-platform library is optimal. The OpenGL and SDL graphics libraries are quite capable.