Kokuto:
Okay. From the drama, I guess I confused him remembering her fathe and his red cloak when he saw her red caped dress, and acting negatively.
My sense was that the reason the Grand Emperor didn't want XY to wear a dress that would make people think she looked like her biological father was that he was afraid for her safety. Which turned out to be a justified worry given that Mu Fei assassinated her after recognizing her as Qi Yo's daughter.
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This is how the Grand Emperor's reaction is described in the novel:
A white long robe with a cinched waist, it made her figure seem lithe and elegant. An outer robe was made out of long gauze with a train stretched long behind her. The outer robe was embroidered with red and black thread into the design of a swallow and peach blossom portrait. When the entire gown was spread out, it appeared that the entire ground was covered with peach blossoms.
Xiao Yao was walking with the long train behind her and was afraid of tripping so she looked straight ahead and walked very, very slow. The cinched waist robe was tightly hugging her waist and she could barely breathe. It made her back ramrod straight and she cursed how this gown was designed to torture her. She pursed her lips and her annoyance was clearly evident in her eyes.
When she walked into court, Ru So and all the courtiers felt dazzled by the peach blossoms bursting behind Xiao Yao as she walked. With her red peach blossom birthmark on her forehead, she was enchanting but for the coldness in her eyes.
The Grand Emperor looked at Xiao Yao and his heart clenched in a long sigh. Right now Xiao Yao looked so much like that person – whether it was the dazzling colors of the world, the endless delights of the Earth, it was all just yellow soil under the feet.
Xiao Yao steadied herself and put her hands around her hips and asked “Dad, how long do I need to wear this outfit at the ceremony?”
Everyone let out a sigh of relief and Ru So felt that this Princess was so cute. But he was also looking forward to the day of the ceremony when the Princess would wear this gown and walk up the high altar tower, with her hair done and wearing makeup, the effect would be infinitely more stunning than today. It would surely strike shock and awe into the eyes of every guest attending from the entire vast wilderness.
The Grand Emperor shook his head “This outfit is no good, make another one!”
Xiao Yao was so happy she almost jumped with glee except for her waist being so tightly constricted that she couldn’t move.
Ru So was gobsmacked. How could this outfit be no good? He looked around and everyone else was just as perplexed. If anyone had eyes, only Xiao Yao and the Grand Emperor thought this outfit wasn’t good.
Kokuto:
Really? What was the Haolin Emperor thinking??? I need to watch that prequel show.
He chose to pursue power at the expense of love, like ZX.
Kokuto:
Well, regret could be part of what we saw in the drama, with him sharing his New Years' meal with a setting for her. And he seemed alone, with his peers, like his Empress gone. Plenty of time to think of what could have been and maybe forget the worst of their relationship, while remembering the best parts.
Yeah. I could be wrong but that's pretty much what I'm thinking based on the info I've found.