Should slides in a deck have boring solid colored backgrounds or images/snazzy backgrounds? Very much depends on 1) your goal, and 2) your audience.

If you are speaking at a conference, big visuals and builds can be quite powerful as they are fun / captivating. For big audiences, the message is as important as its delivery.

If you are speaking to investors or partners, too much imagery can come across as too much 'fluff'. I read dozens of decks each week - as most investors do - and have seen a trend towards text and product screenshots.

I generally believe simpler is better. And I generally like to feel as though more care was put into the content than the colors. Just my two cents!