Snelsi

// Ключевые точки градиента
const red      = [255, 30, 30];
const yellow   = [255, 215, 74];
const green    = [60, 255, 95];
const blue     = [85, 145, 255];

function to_rgb(color) {
  return `rgb(${color[0]}, ${color[1]}, ${color[2]})`; 
}

function blend_colors(color1, color2, percentage) {
  let color = [];
  for (let i = 0; i < 3; i++) { 
    color[i] = (1 - percentage) * color1[i] + percentage * color2[i];
  }
  return to_rgb(color);
}

let bgColor;
if (!value) {
  bgColor = "grey";
} else if (value >= 10) {
  bgColor = to_rgb(blue);
} else if (value >= 8) {
  bgColor = blend_colors(green, blue, (value - 8) / 2);
} else if (value >= 6) {
  bgColor = blend_colors(yellow, green, (value - 6) / 2);
} else if (value >= 4) {
  bgColor = blend_colors(red, yellow, (value - 4) / 2);
} else {
  bgColor = to_rgb(red);
}