- I believe sliders would be a great thing to change constants in a function. It would make changing them more natural, smooth and simple;

Yes, I think I have it on my todo list. I hope some day to get the time to get it implemented.

If you select Custom in the color list, you will be able to choose between 256 colors. It could probably be improved. I might look into that some time.

You can set the axes ranges in the Edit|Axes dialog.

Unfortunately I don't think I will ever get the time to get 3D implemented. It will require a major redesign.

My suggestions goes as follows:
- I believe sliders would be a great thing to change constants in a function. It would make changing them more natural, smooth and simple;
- Adding a color tool to enable users to change the color of functions, points, etc. to any possible one, or simply adding new natural-looking colors, like the ones in GeoGebra, which are essentially "Pastel colors".
- The axis cannot be scaled directly. There is not a setting to scale by 1:100, for example, or any user-defined scale.
- It would be truly interesting to have 3D graphing. The only app I know that does this efficiently is Quick Graph for IOS (iPhone)