Note: Meabe there is already Instrucatble like this, but here is my version.
Step 1: Parts, and Let's Start
*Optic computer mouse
*100mcd 20mA blue LED
So, when you have parts and materials, start workin'. Open your mouse(there is usually just one screw), remove wheel and cable.
Step 2: Locate a LED, and Change It
2.2 - Remove a LED holder.
2.3 - You have a red LED. Unsloder it.
2.4 - Put blue LED in holer
2.5 - Solder it and cut surplus of anode and cathode.
2.6 - Put LED holder and its place on PCB board.
Step 3: Group Mouse and Enjoy!
Untill next Instrucable. David.