The horse of the Hazrat Hussain (RA) which got legendary status after Karbala is part of many legends related to Karbala and has been part of poetry and Art since centuries.
In this thread, lets share some of those paintings (available online or you see somewhere).
The tomb has red flag. Normally, mourning is represented by black and most of the darahs of Indo-Pak also have black or green flags.
Why Roza e Hussain (RA) got red flag. It is said that as per Arab traditions, red flag on a tomb mean that the person (who is buried in tomb) got waris and they will take revenge. After the incident of Karbala, only Hazrat Zain ul Abideen (RA) was alive from Hussain (RA) family and he was sent to Syria. But some tribes, who later buried the corpses in night, put these flags and therefrom the tradition of red flag on Roza e Hussain started.