The heart shape box filled with colors represents his dil and life. He has given his heart to Kalpana hence "this heart belongs to you" wala dialog. And she has filled his life with colors which was filled with darkness and loneliness until she crossed his path.
He was walking the path of revenge but by accident or fate, she was there to stop him walking this dangerous path. He has also helped her to become stronger on his twisted way. Great challenges make life interesting; overcoming them by fighting our own battle makes life meaningful which was taught to Kalpi by Raghav.
I hope we get a Holi segment.
PS! The parallell between Raghav and Pakhi was nice. We saw Raghav trying to reduce the gap between him and Kalpis two different worlds while Pakhi gained information to impress him by being someone she is not.
Don't ever change just to impress and please someone. Change because it makes you a better person and it leads you to a better future.