Yes, they were all the rage (as in all the cool kids had one) when I was at school in the late 1960's. We used to paint all kinds of designs and pictures on the flap. They came in several colors: RAF blue and Army khaki, from various sources.
Some had been recycled and still had the serviceman's name or number on them, many of the ex army ones had been treated with "blanco" paste (which itself came in different shades of green, khaki and white); others were new unissued surplus stocks made in the UK and other countries. Canadian made web gear was different in color to Australian and Indian manufacture (hence the use of blanco paste to give a uniform appearance): Indian made webbing was a distinctive almost yellow shade of khaki compared to the light brown stuff made elsewhere, and often had black or gunmetal fittings instead of the usual brass.
When I am emperor of this galaxy though, I shall institute a rule that every army taking part in a war must us the same uniform all the way from start to finish, not change pattern and color half way through!