The old Cessna airspeed indicators used to have a yellow arc . Top of the arc if you were heavy , bottom of the arc if you were light made Va simple .
i do not understand why they stopped painting the yellow arc on the airspeed indicators .
The yellow arc on some airspeed indicators is not necessarily related to Va. Va will generally be slower than the bottom of the yellow arc. Va is the maximum speed at which the pilot could overstress the plane with large pitch control inputs. Slower than that speed, a large control input would result in a stall, which would automatically unload the stress on the wings. Va is not normally marked on the airspeed indicator, but rather placarded, as it varies by weight.
The beginning of yellow arc on the airspeed indicator is the maximum structural cruising speed (Vno). Faster than that speed, a prescribed gust (by design standard) could overstress the plane without pilot input. Hence the limitation that flight at speeds in the yellow arc be conducted with caution in smooth air only (meaning avoid turbulent air, and don't handle the controls roughly).
The top of the yellow arc is Vne, it is certain that at Vne, you are well above Va at any weight, so you should already be being very gentle on the controls.
For some engines on the Cessna's the white arc goes all the way down to 0. For some it doesn't.
I'm not aware of a white arc on any engine instruments. The white arc on the airspeed indicator is the flap speed limitations, and will extend from full flaps stall speed (IAS usually) to the maximum full flaps extended limiting speed. There may be a green arc on the tachometer, which on most shows the normal operating range for the engine (cruise data provided), though I agree that I have seen some tachometers which at marked green from the maximim RPM (red line) back to zero RPM, I don't know the logic of this. A few Lycoming powered plane with certain props also have a yellow arc within the greed arc, nothing to do with airspeed, it's a propeller vibration caution.