Where are you generally? When it blooms in the season is part of the ID, and whether you are in NH or TX will effect when the seasons are. I am assuming it is blooming now - it that the case?

NYC area. Just finishing up. Grabbed camera to captured last few blooms. Bloomed profusely starting late April. Weather here was cool...below 60 lots of rain.

'Huldine' would be the first to come to mind - an early bloomer with pure white flowers and creamy stamens.

Look at the back of the flower, does it have mauve stripes? Huldine does.

Hmm...these are leaning more towards a pale greenish hue rather than mauve. I only have two flowers left. Wished I would have checked when they were flourishing. Third year for these...was hoping to get a repeat bloom. These are in containers...eastern exposure.

On sale at Bluestone right now should you decide you must have Huldine, she is a big grower, mine gets to the top of a purple leaf plum....

Looks like duchess of edinburgh clematis.

It is definitely not Duchess of Edinburgh. DOE has stacked petals. See picture.

Guernsey Cream? This is one of the white type 2 clems I have been thinking of purchasing...

I wondered about Guernsey Cream also, but mine blooms earlier, and Clematis on the Web says 6-8 petals while the original photo has 9. I haven't actually counted my GC, so I am not sure how likely there are to be exceptions. I think the petals are slightly different in shape in the original photo, but it is possible.

I think it's mme le coultre. I just got one this year. No flowers yet but the leaves look right.

Perhaps 'Candida'

Candida

Or John Huxtable which appears to have more crimped edging on the petals.

John Huxtable

I actually grow John Huxtable... and no, he doesn't look like that, plus his blooming time just starts while ppmary's clem is finishing.

Meanwhile -- if it is not GC, to my eyes Madame Le Coultre and Candida look pretty close, but I can't tell further....

Could it be Toki?

This Clematis bloomed in April in New York COTW says June for Candida....ditto John Huxtable. The shape of the tepals is wrong for Guernsey Cream...