Techniques are provided for illuminating cytological specimens using light emitting diodes (LEDs). In one implementation, a pulse width modulated (PWM) LED source allows for color and intensity adjustment. A user may select the desired color and intensity of light, or the desired color and intensity may be electronically calculated. Using various colors of LEDs, such as red, blue, and green LEDs, various colors can be produced by modulating each LED duty cycle, for example, using a PWM controller.