twilight

Q: What is the definition of twilight? In beheshti zewar English it says the redness on the western horizon, when that disappears then esha time comes in. However some kitaabs mention the twilight according to imam Abu hanifa as the whiteness after the redness. Which is correct. Why is it mentioned as redness in the beheshti zewar, would this not make our esha time early like the shafis etc.