Wear rain gear.
Trolling for salmon in the rain
One of my best days fishing salmon out of my kayak was a cool, rainy July day during the Friday of Salmon-a-rama. I had on my drysuit, so I didn't care about getting wet. It was a perfect storm back in 2016... Wisconsin side had a ton of kings around, but they were mostly in the mid-teens for weight. Myself and a few other kayakers absolutely slayed the kings pulling cranks and spoons in 12-30 fow. I ended up going 16-23 with 14 kings and 2 coho from about 4am-10am. I had 4 kings from 15-18 lbs, 4 more from 12-15 lbs.
2016 was such an odd year - kings would feed all day even out of temp. I was catching them in 40 fow when the water was 60 degrees on the bottom all day in clear, sunny conditions. I felt like a rockstar catching double digit numbers of kings every trip during SAR that year. Last year was a snap back to reality with the numbers crashing back to earth, but the size was so much better.
So to sum it up, I agree with the colors listed below. When there's no sun, I feel like that morning king bite might last a little bit longer as well.
The old saying bright days use bright colored baits, dark days use dark colored baits applies.
In low light situations like rainy days I always found white or pearl colors out performed silver. So spoons with glow paint or tape on both sides were best. Pearl #3 J-Plugs on long leads or leadcore are great too. You may find the fish higher in the water column too.