In this question, a user stated that he bypassed the issue of not having custom colours in math formulae by editing the LibreOffice source code.
Unfortunately, the user I mentioned didn’t explain how he did that. As you can see in the other post, I asked him, but since he has not been online again yet, he could not reply to my answer.
Can someone help me in this regard?
Thanks for your reply, Mike! That looks promising.
But what does that code mean? And how do I set real CUSTOM values? Furthermore, what do I do with that code, now? Where do I have to put which part of that code? And into which file? And where to in that file? What else do I have to do? I have to mention that I’m not a programmer.
From my perspective the only thing you could do is to file an enhancement request for math to support attribute function color color codes like #abdcdef.
Heh, are you asking for a development question (in which case you are expected to be prepared to setup development environment, read the documentation, and given the code pointer above, do some coding), or do you ask that something be done for you (in which case, you didn’t need the code pointer, but needed to file an enhancement request to bug tracker)?
@anon73440385: This has already been done many years ago. But nothing significant has happened, even though someone said that it is generally possible to implement the use of RGB values. See the following links:
https://bugs.documentfoundation.org/show_bug.cgi?id=40436
5156 – colors in formulas
@Mike2: Well, I’m definitely not asking for the latter, since – as I said above – nothing has happened there since ages. So, apparently I’m asking for the former. 
I don’t know. I just wanna know how he has done it. Maybe I can do that, too.
I just wanna know how he has done it
Unfortunately, the user I mentioned didn’t explain how he did that. … I asked him, but since he has not been online again yet, he could not reply to my answer
So - unless he is online to answer, you can’t know how he did that. And if you expect that other answer that, it requires that others re-do the work that that person did, hoping that they understood that person’s idea and result correctly … too much assumptions and work.
By the way: Regina’s change is a better code pointer.
No, I think we’re talking past each other.
But thanks anyway. Maybe someone else can imagine or even knows how he did it.