Sequential Color Map with One Color
This example visualizes light intensity across a narrow wavelength range of 620 to 630 nanometers using a sequential color map based entirely on shades of blue. The display is a horizontal strip of 11 adjacent blocks, where opacity increases with wavelength. The code uses plain JavaScript and the DOM API, creating each block via `document.createElement` and setting its background color through an `rgba` string with varying alpha values. No external libraries are required, and the mapping is linear, with intensity calculated from the wavelength difference.