As stated above, variations in colour shade can occur spontaneously without any (known) genetic basis, or they may be due to known genetic factors which modify the expression of the colour pigments in some way; the latter variations are generally more pronounced than the former. These two forms of modification (shades and genetic factors) can occur in combination and can result in an endless palette of possible colours in the horse; it is often impossible to discern the genetics behind a particular colour without resorting to laboratory tests.