and if everything wont help - the solderings under the graphics processor could be faulty - that was my first thought when i read -> "screen moves from grey with apple logo to solid blue"
that is the moment when the graphics mode change and the funky acceleration should step in - but since the gpu is faulty - it's not possible.
had this "exact this problem at this point) on many g5 iMacs - all had a soldering problem and almost all (except one) are running nicely now.
BUT - do all the software related steps first - my suggestion was only because i thought about that when i read your problem
edit: i have to edit it into my original post - it's to long for a comment
are you sure about that ?
it would countan a lot of hot air and a flux dispenser ;-)
ok - it's not that hard - but since the most people don't have a professional hot air station - i describe it "kitchen table style"
first of all follow the instructions from ifixit to get the logic board out of the case.
remove everything from the board - find the GPU (depends on the model you will fix)
use some flux (don't know how it's called in the us) on the sides of the gpu and the bga chips aroud it (in cas of the g4 iBook they are very close - so use it at all of them)
DONT PRESS ANYTHING ON THE CHIPS!!
lay the logiboard on something heat resistant - but not metal stuff (stone is great - but not everybody has something like that)
then a heat gun - mine goes up to 590°C - but that would be overkill (if you dont know what you're doing) - reduce it to around 270-310°C
but first things first - start with a lower temperature - warm the whole logicboard slowly to the suggested temperature - never stay to long on one spot, never go nearer than 15 cm (as i mentioned before - if you can read solderings and chips - then you can handle this like you want - but thats safer to do it that way if you never did that before)
when the "working temperature" is arrived - heat the gpu area for around 5 minutes (circeling above the chip - not from the side, this would give you a flying gpu and thats not what we all want)
after the 5 minutes, cool down the heat gun and the logic board for about 5 minutes - reduce the temperature slowly and then - go away - let the board untouched for a while - it should get normal temperatures again - and do not ever touch anything on the board until it's "cold" - i think 15 minutes are good - 30 are better
the reassemble everything carefully - the iBook g4 board is to thin for the stuff they put onto it - not that you Kill it while you put everything back togehter.
so - that was it for now ;-)