Use variable in setcustom

[Ergus <spacibba@aol.com>]

Hi I want to have a simple colour palette that must be compatible with
tui and gui.

The problem is that the color names are not the same so for example the
brightblack are not available in gui only in tui.

To work around this I made:

```
(defconst my/colors '((black . "#000000")
		      (red . "#cd0000")
                       ...
                       (brightcyan . "#00ffff")
		      (brightwhite . "#ffffff"))
   "List of colors.")
```

And then I assign the colors with something like:

```
(set-face-foreground 'font-lock-preprocessor-face (cdr (assq 'magenta
my/colors)))
```

But if I try to use a better method for my colors as Stefan suggested:

(custom-set-face ...)

It doesn't work. Do we have some method to define colours or paletes?

So that I could use a similar approach like?

```
(set-face-foreground 'font-lock-preprocessor-face "mycolor")
```

Thanks in advance,
Ergus