well, you're a pixel artist, right?
so you probly know about 8-bit palettes ... 256 color indices that use ids [0..255] ... those lists i linked to are the colors of the ids.
But the lists are not numbered. They are in order, however. the first RGB value is id #0 ... the last RGB value is id #255
So try something like this: in something like Gimp, open the (true) XCOM palette that you want to get the color of. Figure out its id. Then copy the corresponding palette-list (under my link) to Notepad++ so you can see line numbers.
The line numbers in Notepad will be off-by-two, however (one for the palette-header, and two because Notepad will start at 1 instead of 0).
then grab the RGB values of the id you're hoping for, convert them to Hex (that worlddatEditor understands) and try it,
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Or,
open PckView (comes with Mapview2). open a PCK spriteset. double-click a sprite, which shows the SpriteEditor and Palette. Change the palette in PckView to "ufo-geo" and the Palette window should display that palette. Click the color you want and its RGB values should appear in the statusbar ... convert them to Hex and put them in worlddatEditor ...
ps. I haven't tried any of this and it's hypothetical, but in theory it just might work