I have been in Mauritania full time for over 18 months now and I still find the separation difficult between "Pallid heron" and grey heron. I have been to Banc d'Arguin where they breed and have being seeing dispersed birds in Nouackhott including today. It is best to see both sub species side by side for easiest comparison. See the image of the bird today.
The very white bird in your third link looks over exposed. The birds never look that white though the picture is of a "pallid heron".
I don't think the first bird is a "pallid heron". The kodak grey scale is a bit high and the legs on the sub species birds I have seen never get that yellow. Yellowish pink is the norm for an adult.
Ironically I can't determine the bird in the second link. It seems to have been taken at dawn or dusk so the grey scale is difficult to make out. The legs look OK to me though.
Some authorities say that there is never black in the head pattern but I believe that is erroneous. It is often subdued though.
Ask me the same question in a another year and I may have a better answer.
Thank you Rob for the detailed answer. I think that the first two links are of the same observation, and indeed the second one was observed late afternoon at 18:20 (just less than an hour before sunset at that date).