Sorcerers Stone and Chamber of Secrets will have a new version, from a 4k source (although the final film will be in 1080p). This is to have more detail in the footage whilst editing, and therefore be able to manipulate both the color grading and the quality to better match the rest of the series in both color and visual tone. Also, the 4k uses the 35mm as the master instead of the DVD upscale that the Blu-Ray is. Therefore, we get the original colors to play with.
Deathly Hallows will have a 4k edition, and a 1080p 4k source. The original, released version had problems with the dark areas of the grading.
Goblet of Fire is going to have a V2.
Half-Blood Prince will be REVISITED and done from scratch, from a 4K source.