Add Option to Explicitly Set Level of Color

[maclong9]

Describe the feature

Sometimes I have design tokens for a couple of shades of the same color, it would be nice if I could explicitly set those and have the rest generated, example syntax below:

const green = getColors({
  "400": "#61BD93",
  "500": "#127749",
  "600": "#006039",
})

Additional information

• Would you be willing to help implement this feature?