Right now the color palette for formatting regular text (text color and highlight color buttons from top format bar) is much more restricted than what is available for conditional formatting. This makes it difficult to provide a key to users that explains the meaning of conditional formatting, since you can’t reproduce the colours used in the table.
Thank you for the mention of this @Nick_HE. I’ve added it to our tracker and it’s a good example to make a case for it.
(Also, if you’re super into keeping the main formatting controls restricted/basic, then perhaps adjust the conditional formatting colours so at least by default it shows the same options as main formatting bar, with some kind of ‘more colours’ to dig deeper)