Add ocean color variable

[benstigsen]

Currently it's only possible to change colorMax, colorMin and colorNoData but not the ocean color (at least not when reading the README)

[StephanWagner]

Actually, the ocean color is just the background color of the wrapper. You could overwrite that with CSS:

.svgMap-map-wrapper {
  background: #d9ecff;
}

[StephanWagner]

Keeping this issue open as this might me a nice option.