Auto RPM circuit tied to dual color LED?

rpm circuit

Hi, new to the forum, with little electrical knowledge myself, but this seemed to be the place to ask around. I have a project i want to attempt, here are the details:

I want to create an LED lit Angel Eye for the headlight of my car,
(for those of you whom dont know what an Angel Eye is, its the luminated halo or loop around the main projector headlight, often seen on BMWs, and it is entirely asthetic in nature)
I would like to use a dual color LED (specificly blue and red) that would transition (smoothly) between the two in cordination with the RPMs for car.

Wether this be by tapping the wire from the ECU, or directly tapping into it behind the RPMs display, i still dont know how, and dont know the specifics of creating a smooth transition between colors (possibly alternating the two colors faster than the eye can distinguish to create blending effect?)

Specifics are
LED: 5mm, dual voltage
Acrylic Ring, incase anyone wants to know,
car is 2006 Mitsubishi Lancer ES, automatic

Havent been able to find a pin diagram for ECU, if anyone knows where i might find one please say so.
Thanks and if anyone has any advice or ideas for how i might do this, it would be greatly appreciated.

Thanks again!

rpm circuit

Smooth transition can be achieved with PWM (pulse width modulation) ..

Take, for example, PICAXE microcontroller .. One of its fuction is to output a PWM signal in the range of 0% to 100% (controlled by a number from 0 to 1023) ..
If you connect red LEDs directly to this output and connect blue LEDs through an inverter to the same output, while changing duty ratio you will have nice transition from red to blue or the opposite way around ..
The rason I suggested the PICAXE microcontroller is that it also can take another analog (10-bit) or digital signal that is related to the RPM of your car and translate this signal to the duty cycle of the PWM output ..

Info on PICAXE (PIC microcontroller with BASIC interpreter) is readily available on the web ..

Regards,
IanP