I have shape tweened bold Arial text from frame1 to frame 20, they stay motionless and change color.
The problem is that all the characters have been affected by the shape tween and part of their borders have become sharper or become thinner.
It look as if a Rat has eaten Times fonts.
for a color tween, you'll get better results using actionscript to tween your text. using a 3rd party tween class like tweenlite is especially easy. you only need to convert your text to an object (like a movieclip) and you can then tween its color in one line of code.