Color Science and Tools

Colorizer online color format converter
Convert a Color : HEX, RGB, CMYK, HSL
Nix Sensor : CIELAB, CMYK, HEX, RGB, XYZ
Leonardo : Hex to rgb, hsl, hsv, hsluv, lab, lch, and jab (CAM02)
LCH : LCH to RGB
EasyRGB
Color Review Simulate Color for web
Gradient Picker
Color Hexa
0 to 255 Color picker
Converting Color converted to 15 different color formats like RGB, CMYK, HSV, HSL, CIELab, CIELCh Android, Decimal, and YUV
CSpace CIELAB to RGB
Colormine Convert the most complete conversion
MATLAB App, also MATLAB
Excel
Excel
Formula
Color Calculator
Unitpedia HEX, RGB, HSL, CMYK, HSV, Lab, Lch, Xyz, Hwb
Colorhexa
Acute Components
Coolors

HSV/HSL are cylindrical representation of RGB
Problem of RGB: discontinuity of luminance, it is also not based on how the human eye perceive colors. See here or here or example of the effect here and the problem of rainbow color
Problem in HSV
Another explanation
CIELUV Ch (CIE LCh) or Polar Luv is cylindrical representation of CIELUV (and for CIELAB : Polar Lab)
HCL is implementation of CIELUV Ch
Problem of HCL: HCL tends to specify colors outside of the RGB gamut, which means that some sensible choices of HCL values will generate values outside the (0,0,0)-(1,1,1) RGB cube. More worryingly, the HCL->RGB transformation is discontinuous. Although it lies outside the RGB gamut, clamping the transform to the closest RGB point does not patch the seam in the color space. Example of Clamping
HCL to RGB need conversion chain : HCL->LUV->XYZ->RGB
Colorspace with HCL, its Python implmentation
HSLuv, other implementation of CIELUV Ch which fully maps to RGB. HSLuv is just like LCH except that it stretches the saturated colors for each hue so that any saturation coordinate represents a valid color, unlike LCHs chroma coordinate. The downside is that the colors chroma (colorfulness) can change when you drag the hue slider. HSLuv, is based on CIELCHuv, the cylindrical transformation of CIELUV; the LCH in David Johnstone's colour picker is CIELCHab, the cylindrical transformation of CIELAB.
LCH Color in CSS
Colorblind and LCH

Coursera: Information Vizualization
Color by Nasa
Theory of Color: If RGB fits to how screens produce colors, if CIE Lab* fits to how we perceive colors, HCL fits to how we think colors. It is like HSL, but perceptively unbiased.
CIE Color Space, chromaticity
Khan Pixar
Nasa
Color Notes
Colorgen Color for Programmer and this