Not Yet!
The Doctor stumbled into the TARDIS, clutching his side. He'd been hurt, but not too bad. He could heal from this.
'What?'
The glow of regeneration energy was rising from his hand
'But...I'm not that badly injured! I don't need to regenerate!'
It was too late. The Doctor was helpless as his form was changed.
He stood up, brushed himself off and looked around.
'Now why...Oh!'
Realisation suddenly hit him.
'Drained the regeneration energy into my hand after I was shot by a Dalek but...it mustn't have all left me! I only delayed the regeneration! So, even though I wasn't hurt bad enough to regenerate, I did anyway, because the energy was still there!'
He looked around for a mirror.
'Now...am I...ginger?'
A/N: I know it's short, but I wanted to give my theory on regeneration. I've discussed this one with friends, and they've agreed. This shows the regeneration, but also explains any troubles with 11th/12th regenerations, which was a major problem for us nerdlings when Journey's End was aired.