Salaam alaikum
1. Yes, Imam Redha, Imam a Jawad and Imam Hadi were dark skinned according to Hadith.
2. They were rebuked for it
Please read following article for detailed answers
https://www.academia.edu/10349890/Racial_Othering_in_Shi_i_Sacred_History_Jawn_ibn_Huwayy_the_African_Slave_and_the_Ethnicities_of_the_Twelve_Imams