In the RGB representation, (0,0,0) represents black, (255,0,0) represents bright red, (255,255, 255) represents white. Adding primary colours gives the secondary colours: red + blue = magenta, red + green=yellow, green + blue=cyan. This is demonstrated in the following diagram which shows what happens when circular red, green and blue light beams are projected onto a white screen and made to overlap:

Such a diagram is sometimes called a colour wheel. Colours on opposite sides of the colour wheel, such as green and magenta, are called complementary colours.

Some of the above statements, such as green + red = yellow, may surprise you, for your experience mixing paints may seem to contradict this. The explanation is that paint pigments absorb colours, leading to colour subtraction, whereas the above text and the colour wheel describe colour addition. Colour addition corresponds to the way your computer screen works - if the screen's tiny red and green dots are lit simultaneously then you will see yellow. It also corresponds to the way the human eye works - the eye has colour sensing cells only for red, green and blue - if the red and green sensors are stimulated simultaneously then you see yellow. Look again at the diagram, and make sure that you can tell the difference between red and magenta, and between blue and cyan. Note how the diagram correctly shows that when red, green and blue lights (not pigments) are added together, the result is white.

Can you tell what colour the RGB combination (0,255,255) would refer to? This would be a combination of no red + bright green + bright blue, in other words CYAN.

Graphics programs such as Paint Shop Pro define a foreground/stroke colour and a background/fill colour. The forecolour is used by various tools, such as the airbrush, paintbrush, pencil, paint bucket etc. You can set these colours using the materials palette - if the materials palette is not visible you can display it by pressing F6 or choosing View > Palettes > Materials. To change the foreground colour click either of the top two rectangles in the materials palette:

This will open a material properties dialogue with a colour wheel where you can select a new foreground colour. You can also background colour by clicking one of the rectangles at the right of the palette. Clicking the double-headed arrow swaps the foreground and background colours.

When you are working in Paint Shop Pro you can also change the foreground colour using the Dropper tool . Click any part of the image with the dropper tool  to 'pick up' the colour of that pixel and make it the new foreground colour. Instead of using the eye dropper tool you can also sometimes pick up colour (redefine the foreground colour) by Ctrl-clicking the picture but this only works when certain brushes are selected.