If some of the numbers in the grid on the colour palette page look confusing there is no need for alarm (at this stage, anyway!). Each cell in the grid has a number made up of three separate numbers in hexadecimal notation. Hex is a convenient way of allowing large numbers to be displayed or stored in a small space. It is a base-sixteen numbering system (one that might have been invented by extra-terrestrials with eight fingers on each hand). Instead of stopping at nine and going back to zero, we have the extra numbers symbolised by letters. C is twelve and F is fifteen. So the number CC is 204 (twelve sixteens plus twelve) and FF is 255.
So what do the numbers have to do with colours?
The tube in your television produces colour by displaying varying amounts of red, green and blue on the screen. All the colours are built up by combinations of these three basic colours. The tube in your monitor works in exactly the same way. The numbers on the colour chart represent the three colours:- red, then green, then blue. So the number 99CC33 means that red is 153, green is 204 and blue is 51 (this is hex, remember. It can be a very useful system - for example, I am a lot younger in hex!). Mixed together they give a light olive green. The higher the number the stronger the colour. So 000000 is black, and FFFFFF, being an equal mixture of all the colours, is white. An important thing to bear in mind is that when visualising colours, it's not necessary to convert the hex numbers; you soon get used to the long gap between 09 and 10.
If you have sufficient colour resolution, it is possible to use any combination of numbers. So you could have a colour made up of 7845A2. The problem comes when you view this on a computer which does not display that range of colour. If, for example, your computer does not display more than 256 colours, it would not be able to cope with a large area in the above colour.
What would happen in practice is that the computer would valiantly try to approximate the colour by 'dithering'. This is a technique (invented by Seurat!) in which individual pixels of various colours are placed close together to try to give an impression of the desired colour.
Sometimes this works quite well.
Sometimes it doesn't. If this looks like a nice, light olive green square, then you are probably viewing it with at least 16-bit colour.
If you wish to see how it looks with 256 colours, you can re-set your colour resolution by clicking Control Panel, then Display, then Settings. There should be a 256 colour option there, which will involve rebooting your computer. You will then see the green square as a lighter green with a (not quite!) regular pattern of dots.
What all this is leading up to, is that the colours on the previous page are not affected by the colour resolution. They are the colours which display correctly without dithering in either resolution
So if you wish to ensure that when the majority of people view your site, your colours look the way you intend them to look, you will make sure you only use colours taken from this palette.