While a cool idea, I feel like this would be better as an archetype. It's basically just a fighter with a special sword, getting almost the same amount of bonus feats, too. Many of the mechanics are very vague and don't feel well thought out. I also don't think making new rules on how the item gets enhanced is a good idea.
Have you looked at the bladebound magus or the soulknife for ideas? (though I've never been a fan of how they basically give you a free scaling magic weapon)
To be honest, i don't think that your soul blade should be its own class. It feels like a fighter archetype.
If you want it to be its own class, it needs to allow more concepts and be less like the fighter.
For example, why does the soul blade gain this incredible amount of bonus feats? And why can it only take combat feats, when it needs crafting feats to even have its weapon advance? Why does it gain evasion and improved evasion, but has a bad reflex save?
Soul Shatter is far to boring for its name and feels a bit clunky.
Overall you restricted the player too much, either through a lot of set flavour(Colors for transformations, etc), or through the transformation.
What if i want my soul blade to be a shield? Then i am getting no transformation support.
In its current form i would advise you to remake it into a fighter archetype. If you really want it to be a class, you need to broaden the possibilities and reduce the inbuilt forced color flavour.