At the bottom of this thread you can see what a scrap piece of flamed maple looks like on top of a walnut stain.
Tru-oil thread
Here's the pic. You can kinda see my reflection holding the camera.
This pic shows unstained, tru-oiled maple on the left. Unfinished maple in the middle and a light walnut stain under tru-oil on the right.
It's hard to find the truth behind what DYE can be used with tru-oil because so many people call stain, dye and dye, stain so it gets confusing.
I think that water-based anyline dyes will work with tru-oil and water-based stain I know will but it's my understanding that dyes enhance the grain better when applied directly to the wood before oiling than a stain will.
Sorry, a little info over-kill on the stain vs dye since I think you just want the wood look with no color.