Motion #FFFFFF on #4C97FF 2.92:1
Looks #FFFFFF on #9966FF 3.68:1
Sounds #FFFFFF on #CF63CF 3.31:1
Events #FFFFFF on #FFBF00 1.65:1
Control #FFFFFF on #FFAB19 1.89:1
Sensing #FFFFFF on #5CB1D6 2.4:1
Operator #FFFFFF on #59C059 2.3:1
Variable #FFFFFF on #FF8C1A 2.32:1
List #FFFFFF on #FF661A 2.92:1
Custom #FFFFFF on #FF6680 2.81:1
Motion #000000 on #4C97FF 9.97:1
Looks #000000 on #CCB3FF 11.45:1
Sounds #000000 on #CF63CF 10.11:1
Events #000000 on #FFD966 15.36:1
Control #000000 on #FFBE4C 12.72:1
Sensing #000000 on #85C4E0 10.96:1
Operator #000000 on #7ECE7E 11.01:1
Variable #000000 on #FFA54C 10.73:1
List #000000 on #FF9966 10:1
Custom #000000 on #FF99AA 10.38:1
Extension (current) #FFFFFF on #0FBD8C 2.41:1
Extension (planned) #000000 on #13ECAF 13.64:1
Actually, thinking about it now, how did Scratch 2.0 do? Let me test that.
Motion #FFFFFF on #496CD4 4.79:1
Looks #FFFFFF on #8A55D7 4.81:1
Sounds #FFFFFF on #BA41C2 4.54:1
Pen #FFFFFF on #0D9A6C 3.58:1
Events #FFFFFF on #C88331 3.11:1
Control #FFFFFF on #E1A91C 2.12:1
Sensing #FFFFFF on #2AA5E2 2.77:1
Operators #FFFFFF on #5CB716 2.54:1
Variables #FFFFFF on #EE7D16 2.77:1
List #FFFFFF on #CC5C22 4.1:1
Custom #FFFFFF on #632E99 8.81:1
Arguments #FFFFFF on #5A47B1 7.06:1
Extension #FFFFFF on #4B4960 8.67:1
It's a representation of the contrast between the text and the block background.