[MC-126777] Double tall grass and double flowers reduce light level, render darker

Stand in double tall grass and look at the light level using F3.

Tall grass seems to be darker than regular grass, for reasons unknown. Screenshots comparing 1.12.2 and 18w10b attached.

Linked issues

Cannot confirm. Are your graphics fast/fancy? Is smooth lighting on?

Turns out I got this entirely wrong.

...how exactly is this invalid?

It couldn't be confirmed and your comment sounds like you had the graphics settings set wrongly.

Affects 18w14a, which does not seem to be a valid version yet

Seems to be fixed in 18w15a; only affecting affected tall grass loaded from a previously affected version.