There's lots to be said for a dark theme in applications on an AMOLED-screened phone - it's easier on the eyes, especially in the evenings, plus it uses vastly less power. And one by one Microsoft has been dotting the i's and crossing the t's of its core Windows 10 applications in this regard - Weather is the latest to get the option of running in a fully 'dark' theme. See the screenshots below. Note that this application update is so far only available for people on the 'Fast ring', but it'll roll out soon enough across the whole Windows 10 phone family.

Before (left) and after (right), Weather's old Settings screen and light theme and the new screen with the 'mode' option. Hang on, 'mode'? What's wrong with 'theme'??

Left and right, the differences between light and dark theme - with only a slight difference on light-centric displays as here...

...and a dramatic difference on more textual displays as here.

You can grab this update in the Store in the usual way. Note that it'll be marked as 'MSN Weather', a throwback to the old naming system!