From color theory, we know that white is the presence of all colors and black is the absence of all colors. Knowing this, we can deduce that black would be all 0s and white would be all full values.

Name: black;
RGB: rgb(0, 0, 0);
Hex: #000000;

Name: white;
RGB: rgb(255, 255, 255);
Hex: #ffffff;

Following this principle, to get any color within the greyscale, we simply need to provide the same value for each color.

#000000 - rgb(0, 0, 0);

#101010 - rgb(16, 16, 16);

#202020 - rgb(32, 32, 32);

#303030 - rgb(48, 48, 48);

#404040 - rgb(64, 64, 64);

#505050 - rgb(80, 80, 80);

#606060 - rgb(96, 96, 96);

#707070 - rgb(112, 112, 112);

#808080 - rgb(128, 128, 128);

#909090 - rgb(144, 144, 144);

#a0a0a0 - rgb(160, 160, 160);

#b0b0b0 - rgb(176, 176, 176);

#c0c0c0 - rgb(192, 192, 192);

#d0d0d0 - rgb(208, 208, 208);

#e0e0e0 - rgb(224, 224, 224);

#f0f0f0 - rgb(240, 240, 240);

#ffffff - rgb(255, 255, 255);