Check your color tune instructions carefully, orange/yellow is a rich indication 

No need to loosen anything just adjust the #2 nut up or down to suit. 
BTW doesn't your car have a HS4 ? Either or the adjustments are the same.
I do not use a colour tune but have heard the A series always runs richer on two cylinders compared with the others so there is no way to get it perfect you just have to compromise, too rich is better than too lean.

I am still a novice here (learning about carbs and reading every day) and finally picked up a ColoUrTune to look at my burn at idle.  Looking at cylinder 1 and cylinder 4 - #1 is nice and blue and ideal mixture....#4 is bright orange and appears to be lean.

I have started to adjust the jet adjusting nut (pic no.2 in below) on #4 to richen it up and wanted to check with the collective - can I just do this now, or do I need to slacken the choke shaft (maybe 5/16 nut?) in order to adjust that jet screw properly.

I tried turning it up to richen and I did not see any difference in the colourtune...Almost one full turn in fact, so I back it off until I have some advice here.

Thanks for any help you can provide.