My Arrowroot plant has slowly but surely lost variegation, as did my Oyster Plant. I have moved the plants to get more light, less light but I was not able to stop the loss of variegation and colors. From what I've read, the color loss is permanent. Can someone please enlighten me about this reversal?

It is not rare for a variegated plants for reverting in to green, when it happens the green plant will outgrow variegated one and can even suppress the variegated part, so if you leave them unchecked, the variegated part will be lost. For this reason, caring for variegated plants will include removing reverted parts
Near or totally white plants can also appear, but they are less likely to survive, due to less or no chlorophyll.

Moving plants to bright or shade will not help to recover variegation at least not in this plant.

There is still chance that you have the variegated rhizome down there, if you really want to rescue them there is a way; un-pot the plant, divide all the rhizomes, separated and grow them separately. watch if there any new growth that is variegated, and discard those that aren't.

there are also type of variegation that is affected by light/sun or weather/season.. for this type, then environment manipulation will recover the variegation.