General

most of the time, blu-ray only have some minor corrections. for example, in episode 8 of Love Live season 2, in a scene in which the characters look out the window, the colors used in that scene has been fixed in the blu-ray version.
sometimes the tv version is so messed up that the entire scene is redone in the blu-ray release
example: [url=http://www.youtube.com/watch?v=TOfr40OVtZA]link[/url]

Code Geass' blu-rays had redrawn scenes.

Newer anime is a little bit harder to tell the difference. But older anime that was later made into bluray, you can definitely tell the difference.

blue rays are more colourful and brighter

Depends on the TV really. Some TVs are so crappy you won't notice hardly any difference between BR/DVD. Also depends on the show. Older shows that get remastered on Blu Ray look WAAAAAAAAAAAY better, such as Cowboy Bebop and Elfen Lied (own both BR/DVD for each series). Newer shows like Attack on Titan, I couldn't hardly tell the difference for the most part visually and think it's just better audio.
Clannad is another show I own that's much better looking on BR due to more vibrant colors and slightly better detail.

All in all, BR is noticeably superior on most (if not all) anime series'.