> font-lock-doc (#8b2252 or so) definitely still 
> looks pretty different to font-lock-builtin (#7a378b or so) on my 
> system.

See attached.  I'd say that three of the faces shown are quite close in
appearance: 

`font-lock-builtin-face' (":type", ":group")
`font-lock-doc-face'     (the doc strings)
`font-lock-keyword-face' ("defcustom")

But especially the first two of these are close.

The point was also that previously these faces were better distinguished -
`font-lock-builtin-face' was `Orchid', not `MediumOrchid4'.

> Are the colors actually used on your system even 
> coming out as similar hex values to those?

Those same hex values are used on my system.  Those are the hex values
corresponding to the two named colors used: VioletRed4 and MediumOrchid4.