I bought Colortune and have you used it a couple of times. It is a bit inconvenient with dual carburetors. Should have four of those. It is not nice to remove and install it when hot and I'm always afraid of accidentally dropping it. I'm also quite paranoid how long time I can run and tune engine without Colortune getting too hot.
Once it was a big help when debugging my DGV 32/36. Jets were right size, carb had new gaskets, etc. but it was running very rich. I went to exhaust gas analyzer where carb was tuned so lean that emissions were ok. Also ignition timing was checked.
When I started car, I immediately noticed that it was way too lean. There was no torque at low revs. Then I ordered Colortune. Soon it was apparent something was very wrong. Either engine didn't idle or flame was yellow/orange (can't remember exactly, certainly not even slightly blue!) Because I had no ideas left I phoned to carb shop where I bought Colortune. They told to check jets once again. Then I found it: Someone had drilled primary idle jet about 2-3 times as big it was supposed to be! I swapped idle jets and soon color of the flame changed to nice Bunsen blue.
With single carb Colortune can be a good help. Just note intake manifold doesn't treat all cylinders equally. I assume it is best to choose the leanest cylinder and then tune carb so it just gets right Bunsen blue color. Others might be slightly richer but that isn't a big problem.
At the moment my GT has dual carbs and I don't have a synchronization tool so I go to a place with an exhaust gas analyzer and other tools.
Also note it must be quite dark so you can see flame color clearly. And good results may need some practice, of course. Last summer I tuned my DHLAs with Colortune and surprisingly got them quite right but it took a lot of time.
