This site attempts to create color palettes and images, that look as close as possible to what the popular chips by MOS Technology, Inc. (in particular the VIC, VIC II and TED) generate. These have been used in a bunch of amazing computers in the 80s, such as the VIC20, C64 and plus/4.
Special care has been taken to provide controls and a display, that behave the same way as the video monitors of that time. This should enable you to modify brightness, contrast and color in a way that is very similar to what one would do, when setting up real equipment - while looking at chip-specific graphics.
Once you're satisfied with your settings, you may download the palette in PNG format from the gear-menu on the upper-right and use it in pixel apps of your choice.