Hi Javier,
I know it's counterintuitive, but "dark green" and "darkgreen" are not exactly the same color.  Chimera has a builtin list of color names it knows about, which includes dark green (but not darkgreen).  If you use a color name not in its builtin list, it falls back to system color names, which in this case includes darkgreen, but darkgreen is slightly different from dark green -- though visually they probably look identical.
Therefore you need to use this syntax to select dark green:  sel @/color="dark green"
As for the color hex codes, the atom-selection syntax does not handle hex codes, only color names.  You can work around this by defining an equivalent color name, e.g.:

colordef testcol #da70d6
sel @/color=testcol

--Eric

Eric Pettersen
UCSF Computer Graphics Lab

On Oct 13, 2021, at 3:13 AM, Javier Sanchez Utges (PG Research) via Chimera-users <chimera-users@cgl.ucsf.edu> wrote:

Hello, my name is Javier and I am a Bioinformatics PhD student in Dundee. I am using UCSF Chimera v1.14 and I am trying to select residues according to the colour they are coloured in, using the following command for blue-coloured residues for example: “sel @/color=blue”. This works just fine, however, I struggle when using other colours such as “medium blue” or “dark green”.  “sel @/color=darkgreen” does not work. It looks like all colours with a single word name work fine, but 2-word name colours do not. Moreover, I can colour residues using RGB codes, such as “col #da70d6 sel” to colour selected residues in orchid. Nevertheless, “sel @/color=#da70d6” does not work. “sel @/color=orchid” works, though. So, is there a way that I can use two-word named colours when selecting by colours, and also, use RGB codes or other colouring codes to select coloured residues?
 
Many thanks,
 
Javier

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