Actually according to this chart: https://www.mecabricks.com/docs/colour_chart.pdf

...the Mecabricks color for Bright Orange is #F57D23, which actually looks quite fine. So I don't need a conversion to the Brickset value after all: I need to understand why the Collada values aren't the ones listed in that chart? Gamma correction or something?

Yeah that's it. Exported a single Bright Orange brick in Wavefront & Collada, got different RGB values:

Wavefront:

0.9607843137254902
0.49019607843137253
0.13725490196078433

Collada:

0.913098651791473
0.20507873637973145
0.01680737574872402

Any idea why or how to convert from Collada RGB to Wavefront RGB?

Ok answering my own question, looks like gamma correction. Something like Collada^(1/2.2) =~ Wavefront.

Colour values for LEGO elements is a very complicated topic. It is not really public knowledge and everybody is trying to guess something.

Bright Orange 106 has been around for a while and I can confirm that the value given by Brickset is official.
Mecabricks colors have been defined back in the days before some values were know and therefore they may be slightly different.

I may have to update the dae and obj exporters to get similar values.
Collada is currently using the color value converted from srgb to linear space while obj is using the raw values (that you can find in my color chart).

Hope it helps

Today, I will put online an updated version of the workshop so that both obj and dae files have the same values. The values will be similar to my chart.

Nice!