Used to use it on motorcycles, very simple. If you're talking SU on a Minor then absolutely no need for anything other than the built in tuning device.
If that is after a good run as opposed to just starting up for a couple of minutes then either you are using a lot of oil, or your carb is set too rich. Just possibly (c) both
Waste of money! You don't need it with an SU carb. Adjust for 'best idle' - then test with the lift pin..... then a good run and switch off at speed - and pull the plugs for a check. Should be 'biscuit' colour - and no, not chocolate biscuit - or Bourbon...
I've used the colourtune, but then I've had mine since the 1980's (used on all sorts of cars). OK to use on SU carbs - gives you that extra bit of visual confirmation.
George.
'50 Low-light with 918 Side-valve engine,
'51 High-light with Side-valve 918 engine,
'55 4-dr with 803 engine,
'56 Traveller with 1098 engine.