[McHilt]

Seeing all the vids of merlins and DBs I'd say blueish like many before me.
The color of flames indicate temperature and as temperature increases flames turn more transparent (the hottest temperatures are nearly invisible as I remember from chemistry class) but hey, I'm not an expert at that
I think the flames should be more transparent (in case when you'd use blueish flames). They also should illuminate the fuselage just slightly... just my opinion as a draughtsman, from what I've seen in the vids posted.

Anyway, nice feature...

Edit: maybe winny is right about that, efficiency rather than temperature but still