Nice talk in this page already in our wiki docs. Environmental impact, washing machines, population, poverty: Key from a TED Talk
Custom color pins for Leaflet. Use Leaflet.DivIcon html attribute, it allows you to pass a string which is evaluated into a DOM element. stackoverflow 
I found the example a fascinating bit of HTML and embedded CSS. I've modified the example with calc and var expressions in the CSS.
<span style=" --u: 2rem; --half-u: calc(var(--u)/2); --neg-h-u: calc(-1*var(--half-u)); background-color: lightgreen; width: var(--u); height: var(--u); margin: calc(var(--u)/6); display: block; left: var(--neg-h-u); top: var(--neg-h-u); position: relative; border-radius: var(--u) var(--u) 0; border: 1px solid #FFFFFF; transform: translate(var(--half-u), var(--half-u)) rotate(45deg); "></span>