: I see visual design as the top layer of UX, and being part of aesthetic it is a very important one. But I agree that the question will be better answered by the graphic design community.

I see visual design as the top layer of UX, and being part of aesthetic it is a very important one. But I agree that the question will be better answered by the graphic design community.

Also, if I'm perfectly honest, many designers don't pick palettes from arbitrary sets; instead, they often 'borrow' one from a site they like, and less often they use photos.

Anyhow:

Colours in a Nutshell 1

Number of Colours

Use colours conservatively.
Limit the palette to about five colours (one glance limit).
Consider accessibility (don't impart information by colour only, for those with limited vision).

Colour Combinations

Aesthetic choices on the colour wheel are often:

Analogues (adjacent)
Complementary (opposing)
Triadic
Quadratic
Colours found in Nature

Prefer warm colours for foreground element, and cold for background. Light gray is a safe colour (non-competing, good for grouping).

You can see these options in the scheme selection wheels from this very useful site.

Saturation

Saturated

Attention
Excitement
Dynamic

Desaturated

Performance
Efficiency
Professional
Serious (darks)
Friendly (brights)

Which colours you should use for links? It depends how much you want people to click on them. A link such as 'Like me' would probably get a warm saturated colour, whereas an informative link such as 'Powered by phpBB' (you don't want people to leave your site to the phpBB site) would probably get a cold desaturated colour.

Symbolism

There is no substantive evidence for colour symbolism, and it varies greatly between cultures.

[1] Lidwell et al., 2003. Universal Principles of Design. Rockport.