Click flag twice, or the color will show as a tiny line. Just copy and paste a hex color code in. This uses the join block combined with pen. It is simple, really. Typing random numbers in can also create random colors... Some of my favorites are... #a7f112- bright lime green #e7bc19- gold #9966ff- default scratch purple #f96d73- coral/pink #26e2d3- neon teal #3e2274- dark purple Feel free to comment any color codes you like!
You can get codes from https://www.color-hex.com/ I heard of the hex code hack with the join block from someone at my school. I don't know their scratch account though...