Why in the comparison table there are different entries for the same card? What is the difference?
And why some of them are colored with different color?
There is multiple information submitted for the same chips, so they are listed multiple times. It's not multiple listing for the same
card.
They need
more info, honestly.
Take the Radeon HD 5830, for example.
You can't just list "5830", or even "Sapphire 5830". Sapphire made 3-4 different 5830 cards. Each company that released a 5830 probably made multiple ones as well. Not all cards are made the same. Some are sold overclocked. Some sold at stock speeds overclock more than those sold pre-overclocked. Different cards use different memory. There are lots of differences. Listing JUST the chipset doesn't help.
Some 5830 cards released in 2010 may mostly be reference designs. Maybe bad 5850/5870 chips crippled and sold as 5830s that suck up a lot of power and don't overclock well. Ones released in 2011 have more efficient, non-reference designs. Maybe they are 5850/5870 chips that have simply been sold as 5830 chips because of the demand for 5830 chips, so they run cooler and overclock better.
Chip name, Manufacturer of card, model # (plus revision, if possible), manufacture date, then GPU speed, memory speed, Voltage, Operating System, drivers used, miner used, and command-line switches.
THAT would give you a good idea of what card does what.
Regarding colors of entries ... I have no clue.