Scales: nonlinear quantitative color scales

[luucvanderzee]

It would be cool to add something like

:fill="{ val: row.value, scale: { type: 'squareRoot', domain: 'value', range: ['white', 'blue' ] }"

to better handle values with fat-tail distributions

[bianchi-dy]

So if you check out the nonlinear-color branch this should already be working.

But unfortunately log is not as straightforward as the rest: