Anyone from netsblox reading this, the colour you should use is cherry 153 0 0.
Categories need colours so users can tell them apart from other categories. You can choose them from a colour selector or from RGB values, but either way it can be hard to make it not look like existing categories.
When making Hashtables into the new extensions format, I wanted to use a category instead of just using Other. I chose crimson there, but I might have to do it again, so I made a script to collect all of the crayons and sort them by distance to the existing categories.
You can search through the colours by hand, or you can use grep to find ones with a specific type. For example, grep reds colours.txt will give all the reds, and grep -v grays colours.txt will get all the colours that are not grays.
The first time I ran it, I got incorrect results because of not taking into account the light colours. I ran it once, and cherry was the best colour. I removed that one for use in netsblox, and these are my final results. Note that distance between the original colour and the light colour is not considered, which is why white isn't at the very bottom. I still would not recommend white, or really any grey. The next best is the exact opposite, cyan, although if everyone does than every category will be cyan. For example, crimson is 35th out of 90, looking somewhat similar to lists, which is fine because hashtables are similar to lists.
cyans: aqua (cyan), crayon 70, RGB 0 255 255
grays: white, crayon 14, RGB 255 255 255
yellows: yellow, crayon 50, RGB 255 255 0
greens: lime, crayon 60, RGB 0 255 0
grays: black, crayon 0, RGB 0 0 0
grays: gray92, crayon 13, RGB 236 236 236
yellows: rubber duck, crayon 59, RGB 251 225 8
pinks: raspberry, crayon 18, RGB 227 11 93
greens: green, crayon 64, RGB 0 128 0
greens: dark pastel green, crayon 66, RGB 3 192 60
pinks: deep pink, crayon 15, RGB 255 20 147
pinks: amaranth, crayon 19, RGB 229 43 80
pinks: hot pink, crayon 16, RGB 255 105 180
yellows: gold, crayon 57, RGB 255 215 0
pinks: bright pink, crayon 17, RGB 255 0 127
grays: gray7, crayon 1, RGB 18 18 18
purples: magenta (fuchia), crayon 95, RGB 255 0 255
reds: red, crayon 20, RGB 255 0 0
greens: dark green, crayon 65, RGB 0 100 0
reds: candy apple red, crayon 28, RGB 255 8 0
yellows: dark goldenrod, crayon 52, RGB 184 134 11
cyans: deep sky blue, crayon 77, RGB 0 191 255
cyans: cerulean, crayon 72, RGB 0 123 167
purples: x11 purple, crayon 94, RGB 160 32 240
yellows: egg yolk, crayon 58, RGB 254 227 62
browns: brown, crayon 36, RGB 150 75 0
purples: grape, crayon 92, RGB 111 45 168
purples: purple, crayon 98, RGB 127 0 127
greens: emerald, crayon 67, RGB 80 200 120
greens: forest green, crayon 63, RGB 34 139 34
greens: mint, crayon 68, RGB 62 180 137
browns: golden brown, crayon 37, RGB 153 101 21
blues: denim, crayon 84, RGB 21 96 189
blues: midnight blue, crayon 81, RGB 25 25 112
browns: chocolate, crayon 31, RGB 123 63 0
yellows: sandstorm, crayon 55, RGB 236 213 64
reds: crimson, crayon 26, RGB 201 0 22
blues: cobalt, crayon 83, RGB 0 71 171
blues: blue, crayon 80, RGB 0 0 255
browns: cinnamon, crayon 38, RGB 184 115 51
purples: dark magenta, crayon 99, RGB 139 0 139
purples: dark orchid, crayon 96, RGB 153 50 204
browns: saddle brown, crayon 30, RGB 139 69 19
reds: coquelicot, crayon 29, RGB 255 56 0
blues: cornflower, crayon 88, RGB 100 149 237
grays: gray14, crayon 2, RGB 36 36 36
purples: indigo, crayon 93, RGB 75 0 130
purples: violet, crayon 90, RGB 128 0 255
grays: gray85, crayon 12, RGB 218 218 218
greens: apple green, crayon 61, RGB 141 182 0
cyans: azure, crayon 79, RGB 0 127 255
browns: chestnut, crayon 34, RGB 149 69 53
oranges: pantone orange, crayon 41, RGB 255 88 0
blues: dark powder blue, crayon 82, RGB 0 51 153
cyans: dodger blue, crayon 78, RGB 30 144 255
blues: navy blue, crayon 85, RGB 0 0 128
grays: gray50, crayon 7, RGB 127 127 127
blues: steel blue, crayon 86, RGB 70 130 180
cyans: teal, crayon 75, RGB 0 128 128
oranges: ochre, crayon 47, RGB 204 119 34
browns: sepia, crayon 33, RGB 112 66 20
yellows: mustard, crayon 56, RGB 255 219 88
yellows: saffron, crayon 54, RGB 244 196 48
reds: sanguine, crayon 24, RGB 192 0 0
cyans: light sky blue, crayon 76, RGB 135 206 250
blues: slate blue, crayon 89, RGB 106 90 205
browns: copper, crayon 39, RGB 210 105 30
cyans: iceberg, crayon 73, RGB 113 166 210
cyans: dark cyan, crayon 71, RGB 0 139 139
oranges: spanish orange, crayon 44, RGB 232 97 0
reds: burgundy, crayon 21, RGB 144 0 32
browns: kobicha, crayon 32, RGB 107 68 35
browns: dark brown, crayon 35, RGB 101 67 33
oranges: tangerine, crayon 49, RGB 242 133 0
grays: gray43, crayon 6, RGB 109 109 109
oranges: orange, crayon 40, RGB 255 127 0
grays: gray21, crayon 3, RGB 54 54 54
oranges: carrot, crayon 48, RGB 237 145 33
reds: maroon, crayon 25, RGB 128 0 0
grays: gray64, crayon 9, RGB 163 163 163
oranges: burnt orange, crayon 45, RGB 204 85 0
oranges: sinopia, crayon 46, RGB 203 65 11
grays: gray71, crayon 10, RGB 181 181 181
grays: gray78, crayon 11, RGB 200 200 200
oranges: pumpkin, crayon 42, RGB 255 117 24
yellows: goldenrod, crayon 53, RGB 218 165 32
grays: gray36, crayon 5, RGB 92 92 92
reds: dark candy apple red, crayon 23, RGB 164 0 0
grays: gray28, crayon 4, RGB 72 72 72
grays: gray57, crayon 8, RGB 145 145 145
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