Very Basic Question

I am wanting to change the LED's in some alarms I have.

I have ordered some blue leds with a cathode and anode connections. The board that they need to be connected to has two wire sone red and one black.

I am persuming that the black wire is negative and the red wire is postive.

The question I have is to what does the cathode connection on the led get connected to and vice versa.

many thanks

Cathode - Neagtive (Short lead on LED) (black).
Anode - Postive (Long lead on LED) (red).

Are you sure that the blue LED will work in place of the LED? They have a voltage drop of about 2.5v over Red's voltage drop of ~1.6v.