Kajol is supposed to be an average, 28-year-old girl. I remember in one of the initial episodes, she even had a dialog saying 'I have no illusions about my own looks, I know I am avg.'
So she is average. But in ITV serial world, they need a beautiful actress to play the FL or no one will watch the show. Very few ITV shows use dark-skinned girls as leads, and nowadays, looking at the casts, they are getting fairer and fairer 
As a side note, I had the same gripe about Mission Mangal movie. The actual ISRO scientist ladies that worked on the project were average-looking women with wheatish-brown complexions. The movie was entirely whitewashed, with Sonakshi, Vidya Balan, and other pretty actresses (all fair-skinned) playing the leads. It was such a letdown for me being a dark-skinned girl myself 🤔.
Edited by monalidp - 4 years ago