I suggest you create, and save your images in their full-colour splendour, probably using PSP's own .pspimage format to preserve any layers, etc.
Then, use the JPEG/GIF/PNG optimizers to generate additional cut-down versions for use on the web. That way, if you decide you want to raise/lower the quality of the images in the future, it's easy to do so.
Bear in mind...
JPG images are always full-colour (well, unless you make a grayscale one), you make them smaller by increasing the amount of compression in the algorithm - overdo it and you get extra lines showing up around all the edges in your image. You tend to use jpg for photographs.
GIF images have a limited pallette of colours, and you can reduce file size by lowering the number of colours. You tend to use Gifs for icons & diagrams.
PNGs can be either limited pallette or full colour, you can use them for almost anything.
"Web safe" colours are completely irrelevant in the 21st century - they only apply to people using 256 colour screens, and when's the last time you saw one of those?
-- Chris Hunt
Webmaster & Tragedian
Extra Connections Ltd