Flame Point Siamese Cat – photo ©bonsaibutterfly
Siamese Coloring depends on whether your talking about the Traditional Siamese cat, the Modern Siamese cat, a type in between and whether the cat is purebred or not and whether you're concerned about complying with cat association standards.
There are many lovely Siamese cats that miserably fail cat association standards and have slightly dodgy pointing etc. These are Siamese mixes, non-purebred. These cats commonly have the classic seal pointing (dark brown, black looking). The original Siamese cat imports to the West were seal point. Most people seem also to keep the Traditional Siamese. Sometimes the pointing is not pure (broken).
But you've really got to start at the top and that is the Cat Fanciers Association's breed standard. The CFA doesn't recognize the original type of Siamese cat, the one we know. For them the Siamese cat is the super slender and long cat with a thin head. This cat, if she is a show cat, is allowed to have 4 types of Siamese cat coloring (pointing). They are the classic pointing colors of seal, blue, lilac and chocolate.
See a chart on this page (opens to the main website and the traditional Siamese - scroll down). Interestingly, The International Cat Association (TICA) who have recently decided (wisely) to recognize the Traditional Siamese, place (as far as I can see) less restrictions on pointing color. So their standard on the Thai (Trad. Siamese) is both traditional and modern in the opposite way to the CFA (Modern conformation, traditional pointing).
TICA recognize both the Traditional (called the Thai now) and the Modern (called the Siamese). For the Thai there appears to be no restriction ("appropriate for color class") and for the Siamese the rule is "all pointed colors". I tend to limit the discussion on cat associations to the USA as there are conflicting views worldwide as to breed standards and cat breed classification. Plus the US is by far the largest domestic cat "market".
However, a quick check on the UK premier registry (GCCF) tells me that they allow a wide range of Siamese cat coloring. They list self-pointed - meaning solid color pointing as opposed to broken pointing (tabby), tabby-pointed (the agouti gene having an impact on the pointing), tortie-pointed (tortoiseshell affected pointing).
The self-pointed cats under the GCCF standard would appear to cover a very wide range including, but going beyond, the classic 4 allowed by the CFA (above). You can see a posting about pointed cats generally (not restricted to the Siamese) by clicking here. More Siamese cat coloring - click this link to see more of Whitaker (heading this post) a gorgeous Flame Point Siamese cat and this link to see a Lynx Point Siamese cat.