In the DV25 codec, for every four luminance samples, each color-difference component is sampled just once (a 4:1:1 chroma subsampling scheme). In a 4:1:1 scheme, the Cb (blue-difference) signal is sampled at the same location as the first luma sample, and then that Cb colour value is repeated three times (while the luma signal is sampled at each of those points). The Cr (red colour-difference) signal is also sampled once and repeated three times.
This co-siting creates a Y/C delay that can appear as blockiness or lower resolution in scenes with high saturation, and particularly red saturation.1
Can it be fixed?
No, sub-sampling artifacts cannot be remedied.
Adam Wilt, The DV, DVCAM & DVCPRO Formats, 2000-2006.