Why were silent movies black and white?

We tend to take modern technology for granted, as it is all around us. These things need time to develop and be invented.

The reason why the early films were in black and white, is the same reason as there was no sound.

It just hadn't been invented at that time.

At the same time as they hadn't got the technology to add sound to film, they also hadn't got the technology to make films in colour.

Sound came first and then colour.