I know it's rude to say this, but I hate that my aunt colors her hair.
Is that so? Why do you hate that she colors her hair?
She's trying to look younger but the color seems off, it never looks very good.
It is not that big of a deal to color your hair and maybe it makes your aunt happy. It makes no sense for you to let yourself get upset over a minor thing like this.
I think she should know that people think it doesn't look good. I'm not the only one that thinks that.
I know you don't like it, but if it makes your aunt happy, let her be happy. Tell her the hair color looks good and makes her look younger. She'll love to hear you say that.