Tassos yes it it a damp species, I grow it in the following mixture a composted bark (neutral ph) 60%, perlite 20% and horticultural grit 20%, I then top the pot of with a layer of horticulture grit which is what you can see. I also add rootgrow, see this thread on the Terrestrial Orchid Forum
http://forum.terrorchid.org/viewtopic.php?t=1012 .
The yellowness is only on the new flowers the old are white, not sure what causes that, definitely not caused by high temperatures here, nothing over 25C this year and that was only for a couple of days, lucky if we get into the high teens. saccifera should be able to take high temps, I have had a big problem with a virus on mine for the last few years
http://www.srgc.net/forum/index.php?top ... #msg200605 and download the PDF, which has decimated my Dactylorhizas over the last few years I hope this is not what you have as nothing seems to clear it.