well, i tried it and it worked very well: Rainbow effect with RGB LEDs using 3 TLC5940's controlled by an ATtiny85 ƎR - YouTube
thank you for sharing it! 
i had some problems because you suggested not to use millis and delays, but i see that the problems are caused only by delays, so we can use millis and micros... we just need to do the update method very often, right?
i've a question, i'm not an expert of making libraries, but to make this library work in an attiny84 do i just need to add this line?
#if defined (__AVR_ATtiny85__) || (__AVR_ATtiny84__)
or is there some register settings to do?
thanks again