Air Conditioning - Replacing Thermostat

I bought a Honeywell CT8775C Digital Manual Thermostat to replace an old Mercury type Thermostat today, In removing the old one, I see four wires coming out the hole in the wall, a red, a green, a white and a blue. The one that concerns me is the blue wire and the yellow wire, both are connected to the Y terminal. The other end of the yellow wire is soldered to the back of the printed circuit board thats attach to the wall plate. Since there is no yellow wire on the Honeywell, should I just go ahead and connect the blue wire to terminal Y? Appreciate your help.

Did you look back at the furnace to see where the blue wire goes to? do you have A/C?

Red is power R
White is heat W
Yellow is cool Y
Green is fan G
Blue is common C

Trace out the wires to the heater and the condensing unit. If there is four wires (r) red is 24 volts Hot, (G) green turns on indoor fan during cooling, (W) white turns on the heat, (Y) bring on cooling, blue may be used if there is no yellow available. I have found many jobs that the colors were not followed as per manufacturer.

Pete