Hello, i have problem, when i use smudge tool in Photoshop and using this tool for making shadow. And when i zoom in, i have so many colors, but when i watching tutorial digital art, when he using smudge tool, He's fine without different colors.
Are those colours actually in your document or just your display? Check with the eyedropper tool and the info panel.
If in your document and you are using 8 bits /channel for your document, convert to 16 bits/channel mode before using the smudge tool. You could also add a little noise which can be very effective at hiding such an issue.
If the issue is just in your display (i.e. it is not shown by the eyedropper and info panel) then short of using a 10 bit/channel display there is little you can do.