Contrasting two yarn crotcheting

[here to stay]

While in a waiting room for a medical test, I watched a woman crocheting a hat with contrasting yarns. She hooked one color, using a finger to hold the contrasting color close to the hook but on the underside. She then caught that thead to hold it when she hooked with the first collor.
I had done such crotcheting but never caught up the alternative colored yarn so I was limited by the length being left free before I picked it up again. Those can get snagged so easily.
What was amazing was that the contrasting color did not show through on the front. The reverse looked like little dots of contrast in the field of the other color.
I was called away before I coul figure out exactly what stitch she was doing. It was a double something.
So anyone know what this is called so I can get more info on it?

[chickenista]

Sometimes it's called 'carrying the yarn'.
You basically crochet Color A around Color B.
It makes a thicker project as there are 2 strands involved.

And she was probably doing a Double Crochet?

[here to stay]

I was thinking a half double but couldn't really tell.

[chickenista]

Half Double crochet is a thing too.
It makes a lovely stitch.