I try to paint with a color and it shows up on the canvas as the color on the opposite side of the color wheel. But if I save the file as an image, it shows up as the correct color. I have tried deleting the program and reinstalling it or a different version, but it doesn't go away.

More information would be of help for this problem.

What Operating System and which version of Krita are you using?

What is the colour space? Do you have just a simple layers arrangement with Normal blending mode? Which tool are you using? Is it the Freehand Brush tool or another tool? Which brush preset are you using? Have you edited the brush preset in any way? Does this happen with all brush presets? Have you made any configuration changes at all?

Can you post a screenshot that shows the Brush Presets, Toolbox and Layers dockers and the entire Krita window?

When you "save the file as an image", what type of image did you save it as?
When it shows up as the correct colour, is this on the krita screen in the original file as soon as you save it, or is it in the saved image when you view it later? Do you view the saved image by opening in Krita or do you use another image viewer?

Reinstalling Krita will not reset any configuration changes that you may have made with a previous installation. This is so that people can keep their customisations after an upgrade.

If you want a totally 'fresh' installation, you need to delete the resources and configuration folders and files after you uninstall Krita and before you reinstall it. The location of these depends on which operating system you are using.

Here is more information about that: https://docs.krita.org/KritaFAQ#My_reso ... te_them.3F

It might also be a GPU problem, in which case change the settings in settings->configure Krita->display, with first trying to switch between angle and opengl, and otherwise disabling opengl all together.

OK. So I'm using mac and the latest version of Krita, 4.0.1 or something. I deleted all the configurations from my library and also all the backup files, then reinstalled it, which didn't work. I haven't edited any of the brush presets and am using a normal blending mode. When I save the file as an image (png, jpg, etc) it shows in the image as the right colors, but not on the program.

As Therahedwig wrote, try to disable canvas acceleration. If that makes the difference, you GPU drivers are broken. That happens with some macs. If so, please make a bug report with full information from help/system information for bug reports. We might not be able to reproduce the issue or work around the driver bugs, but we do need the data about broken systems.