I want to replace a grossly inaccuate thermostat (ITT w/ 2 separate dials) and the wiring coming to the thermostat has 6 wires; green connected to (G), black connected to W1, blue to RC, red to RH, yellow to Y1, and white to Y2. Is this a multi stage issue?
The Programmable electronic one I purchased from ACE HDWR shows 5 wire config. not a six.

Please give advice!

Well it looks like there is 2 stages of cooling from the Y1 and Y2. What equipment do you have? BTW your color code is off.