[css-color-5] Validate color profile components case-insensitively

[cdoublev]

The current text is not very explicit about whether the components descriptor should be invalid when it includes a component called NONE:

A component must not be named ‘none’, [...]. If this descriptor contains a component called ‘none’, the descriptor is invalid.

I propose the same wording than for custom counter style names:

<counter-style-name> is a <custom-ident> that is not an ASCII case-insensitive match for none.

I presume that case-insensitive component names are not wanted.