Weak flywheel magnets CAN NOT GIVE YOU blue , white or violet spark specialy if you take measurements inside the cylinder the color of the spark show the condition of the system flywheel + coil and if one of theese two have problem then you dont have the above colors .
for measure the flywheel magnets you must have Gaussmeter or put some iron powder on the magnets if this powder go to the ends of magnets ( poles south - north ) then you have good flywheel magnets , if this powder stay in the midle and dont move then you have weak magnets not 100 % proove method but give you a idea
if you use Gaussmeter the higher result means the better magnet