I never made the connection either, until it was pointed out to me that this is basically shown in the intro section? And this is when the tree stops showing up and suddenly flower lady is very present.
But... but... it... they act like completely different people?! Obviously the CGI plant is Ying Chun's twin sister, since twins seem to be going around a lot.

Hmmm. I was tempted to nod along, but I'm actually not sure I'd put it in the realm of 'issues'. It's more like, this was a big secret, and he knows Zhao Yunlan has been pissed off about the secrecy, and he's terrified he's going to lose Zhao Yunlan. As I'm thinking this through, I think this might be more related to his 'black-and-white/stark demarcations/once you're out you're out'** approach than abandonment issues. He doesn't have much of a framework to know that Zhao Yunlan could be pissed as hell at him, but the reason he's pissed in the first place is that he cares, and can get over it.
I ... guess? Tbh I think I file a large chunk of that under abandonment issues.

Re: the hair color ... yeah, I can see that. It might be Zhu Yilong having dyed his hair for his last job and not dying over it with black? In-universe, we'll just have to decide that he accidentally bought the wrong hair care product instead of shampoo. Or that it was a prank/dare/department Christmas party thing. Or Shen Wei thinks it makes him look more human and relatable!