I also believe a solar cover will increase your pool temps over the course of a sunny day - even a blue cover. I see it every day, and this season in particular have REALLY kept an eye on it because of all the controversy in this forum last year.
Here's my case:
My pool - 30 foot round (pool A)
Neighbour's pool 24 foot round (pool B)
- both located in identical locations 300 feet appart - full sun all day
I use a cover, neighbour tossed his due to age this spring.

Springtime - I didn't cover either - pool temps identical all the time every day.

Once we got pools cleaned up, we both started to run the timers 9-5 on our pumps, I covered my pool up. My temps slowly started to increase, maybe half to full degree per day, some of that heat was retained overnight - yes, but every day I gained on his pool over the course of the day. after about 2 weeks, my pool was 7 degrees warmer.

If I leave my pump off for a sunny day with a blue cover, the water for about 4-6" under the cover is about 98 degrees, once I turn the pump on for about 3 hours, the entire pool has averaged an increase of about 4 degrees - my neighbour's on the other hand may pick up 2 degrees in that same day without a cover.
remember that evaporation cools while the sun heats, with a solar cover, you don't get the evaporation - therefore, more heat gain.

project is now canned since I fixed my solar panels and they are now operational, so any further comparison is not accurate anymore.

I also believe that the darker blue actually attracts a little more heat than a lighter blue liner would. - a black cover would attract even more, as long as it's able to transfer that heat through to the water it is in contact with, your pool would definitely heat up more.
A clear cover would allow the entire liner (walls and all) to attract heat and because of the cover, almost no heat is removed due to evaporation - I have yet to find out which cover is best - clear - blue or black, however, I truly feel after this spring that a cover is certainly more advantageous than no cover.

One last benefit you have with a cover is that you're not topping your pool up nearly as much as without a cover, and when you add water from the hose, it's really cold (about 65 degrees) compared to the pool water which could potentially lower your entire pool temp by about 1 degree if you need to add 3 inches.