Why don't you just let it weather naturally? It will be weathered gray in a couple years.

It will be weathered gray in a couple years.

Or less. And it will look better than an artificial weathering job.
HOWEVER, your wood will not last as long as if you used a stain or other coating.

Here are a couple links of interest. Keep in mind that this organization exists to promote sales of cedar.

www.wrcla.org/pdf/WRCLA_Guide_to_Finishing.pdf

www.wrcla.org/pdf/Finishing_WRC_Siding_Solid_Stains.pdf

red cedar will not give a weathered grey / driftwood look
white cedar will under ideal conditions ( like cape cod with no roof overhangs )

if you want a weathered grey you need a stain ... bleaching oil will not turn a red cedar to grey

if you want a wethered grey , use a wc and a bleaching oil... or pick a stain you like
a pretty successful treatment in coastal areas is a mix of bleaching oil and silver grey ( Cabots )
best bet is a factory treated WC shingle like SBC

the stain will preserve the shingle far longer than an untreated shingle... it will preserve it practically forever if you renew the stain

red cedar is a more formal look, and a more stable siding.. it will not curl and cup as much as WC
however , the factory treated WC are almost as stable and pretty much replicate the formal , straight lines associated with Red Cedar R&R

red cedar will not give a weathered grey / driftwood look

Seriously? It doesn't weather to a silvery-gray look?

What does it do where you live?

some turn brown...some turn black...some turn  dark grey.... none turn silver grey
the color mostly depends on two things.... sun exposure and rain runoff

and  you will not get a uniform color on the same house...it will depend on the sun exposure  .... the ones in partial shade will be adifferent color than those in  full sun

some turn brown...some turn black...some turn dark grey.... none turn silver grey

Which is where?

Here in the Pacific Northwest, it's gonna turn silvery-gray, although I'm sure it is possible to have a different outcome once in a while.

We know this from 160 years of using lots of WRC.

coastal Rhode Island... the epi-center of Shingle  style architecture

I would guess that  25% of the houses in our island community are WRC....  the only consistently grey  shingles  are on the north side of the buildings

"It is important to understand that the choice not to apply a finish to your cedar product has longterm implications. This choice requires advance consideration before you allow natural weathering to begin. As Western Red Cedar weathers, it will lose its natural color and become grey. In very dry climates, it weathers to a silvery grey color, but in most other climates, because of varying moisture and sun exposure conditions, the Western Red Cedar does not weather uniformly and is likely to develop a dark, blotchy, grey appearance. " http://www.wrcla.org/pdf/WRCLA_Guide_to_Finishing.pdf