Looks like colour glaze but Royal Oak mark...

This one is beyond me... I have seen Daniel Steenstra planters with the Royal Oak mark, but a PLATE? This looks exactly the same shape and glaze as the early colourglaze, eg the Roydon South Pacific plates. Ev have you found any info about a crossover between CL and Royal Oak? This is from the wonderful Jim's collection.

That is amazing!
I will have to do some sleuthing to see if I can find any clues regarding that one as I really don't think that Royal Oak made that sort of tableware!

I could be dreaming but.... the font and style of the text on this Crown Lynn mark looks very similar to the Royal Oak one... this is on the plate also shown below.
 

Gail Henry has this mark on page 237 2nd Edition and says it is from circa 1975 - 1979 and was used by Royal Oak .......
I guess this should then go into the Royal Oak Gallery, but my goodness it looks purely Crown Lynn to me, like they made it and put the stamp on for Royal Oak. Perhaps you could find out some details about this ware and the planter that has the same mark Val.

Ev I am glad you have pulled this one back from the depths... Hoping to look into it in a few weeks

I'm popping this Royal Oak Potteries yellow bowl into the Royal Oak Gallery as it's an oddity to date.  Perhaps some more info will turn up ....?