Ask Mr. Smarty Plants

If you follow this link to our webpage on Oenothera speciosa (Pink evening primrose), you will see that it shows both white and pink as bloom color. On that same page is Bloom Infomation:

"Bloom Color: White , Pink
Bloom Time: Feb , Mar , Apr , May , Jun , Jul
Bloom Notes: In southern parts of its range, blooms tend to be darker pink or rose and to open in the morning. Northern populations are often paler or white and night-blooming. An average coloration would have shell-pink blooms that transition to white in the center and are veined in a deeper pink. Flowers release a scent starting at dusk. In the most southerly parts of its range, from Chihuahuan Desert grasslands to northeastern Mexico, blooms whenever temperatures are above freezing. Elsewhere, blooms heaviest during spring, with blooms diminishing in size as the weather gets hotter. Each flower lasts only a single day."

Since the blooms last only a single day, we are inclined to agree with you that the white blooms you observe could not be faded pink blooms. Here is another article on the white evening primrose.  These bloom at night and attract night-flying pollinators.