To use a colour in a template or table you can use the hex triplet (e.g. bronze is #CD7F32) or HTML color names (e.g. red).
Editors are encouraged to make use of Brewer palettes for charts, maps, and other entities, using this tool.
To make a word have colour, use:<span style="color:hex triplet or colour name">text</span>
Note that you can't use the British spelling, "colour", in this context.
Examples:
<span style="color:red">red writing</span> shows as red writing<span style="color:#0f0">green writing</span> shows as green writing<span style="color:#0000FF">blue writing</span> shows as blue writingTemplate:Font color, or its redirect Template:Font colour, can also be used.
{{Font colour|fontcolour|backgroundcolour|Your text here}}
Wikipedia uses this colour scheme on its Main Page.
And additionally on the Community Portal:
Additional 3-colour palettes using this same generation scheme are at the top of the talk page. In the Monobook skin, the background colour of Wikipedia pages is #F8FCFF. In the Vector skin, the background colour on all pages is #FFFFFF.
The Wikimedia Commons uses this colour scheme on commons:Main Page and commons:Help:Contents. Differing from the English Wikipedia, Commons does not use an extra, darker colour for bordering the header. Also, the colour sets are not derived from a hue the way the above table does.
Approximately 1 in 12 men and 1 in 200 women with Northern European ancestry have red-green colour blindness; this and other types affect people worldwide.[1] This table shows "safe" groups of colours which are distinguishable to most colour-blind people, although colour should never be used as the sole method to convey information.
See also Commons:Commons:Creating accessible illustrations for color blind friendly palettes.
The following utilities may be of use in determining whether a revised image is distinguishable to colour-blind users. Typically they take a web page or image file as an input, and render a colour-blind simulated image as output:
The standard rainbow should not be used to represent continuous data, because it creates artificial thresholds; humans do not see the spectrum as a smooth ramp. Greyscales, or a perceptually-even colour ramps, or a colour map chosen to deliberately highlight certain features, are preferable. Diverging colour ramps (two colour extremes around a white or black neutral value) tend to hide some high-frequency features.
Colours have cultural connotations; pick ones that match your data. That is, a diverging colour ramp with extremes "hot, cold" will be easier to understand than the reverse (hot, cold).