[pikevi]

I just have the basic knowledge of Botany, viper.

But appearence of red pigments in 'usually' green plants is due to depletion of chlorophyll. Almost all plants have many pigments (anthocyanins,in this case, which is the red pigment) and many others. But chlorophyll will mask their expression. When the amount of chlorophyll is reduced( as in fall season) the other colours show.

Some chemicals and reduced oxygenation of the roots also can cause a reduction of chlorophyll production.

I am not sure if it is something other than adequate lighting in your case. May be some dendrobiums do exhibit redness. Check the amount of light it receives.

I hope someone will help you more.