replace rgb codes with CSS colors including plotly recommended colors

[rl-utility-man]

this PR is entirely trying to apply the following expectation. I often chose CSS colors closer to those in the original graphics even if they were not on the plotly list ....

• [X] Hex codes for colors are not used in any new/modified example in favour of these nice ones ...

[rl-utility-man]

Before the Plotly team takes too much of a look at the details of this, I'd welcome a conversation about whether to expand the scope of this PR to address other non compliance in this page (e.g. hardcoded data) and whether this is worth pursuing at this time. I could also close out this PR and replace it with a PR targeting just hex code colors in 6 files in the docs. Hex codes are rarer than rgb colors in the docs.

[gvwilson]

thanks @rl-utility-man - I'll merge this in as part of 6.2.

[LiamConnors]

thanks @rl-utility-man