Ask Mr. Smarty Plants

There are five species of native Delphiniums that occur in Montana:

• Delphinium bicolor (Flat-head larkspur)  You can find a dark pink photo of D. bicolor in Montana Plants on FlickRiver.  ColinHerb.com shows a series of photos for a pink variant D. bicolor
• Delphinium depauperatum (Slim larkspur)
• Delphinium glaucum (Sierra larkspur)
• Delphinium nuttallianum (Twolobe larkspur)  There is a pale-colored D. nuttallianum at CalPhotos.
• Delphinium x occidentale (Duncecap larkspur)  You can find photos of pale-flowered and pink-flowered duncecap larkspurs from the Teton Chapter of the Wyoming Native Plant Society and CalPhotos.  This plant is identified as a hybrid between D. glaucum and Delphinium barbeyi (Subalpine larkspur).

Delphinium ajacis [synonym = Consolida ajacis] (Rocket larkspur), a European native and a cultivated species sold for flower gardens that now occurs over a large portion of North America, including Montana, can be found in a variety of colors—purple, light and dark blue, light and dark pink, and white.  It is possible that you might have found one of these non-natives, but I am inclined to believe that you found a color variant of one of the natives.

Here are descriptions of several of the species above from eFloras.org, Flora of North America online, that might help you determine which native species it was:

D. bicolor, D. depauperatum, D. glaucum, D. nuttallianum,

D. nuttallianum lists the flower colors as:  "Flowers: sepals usually bluish purple, rarely white to pink,..."  All the others list the sepals as blue or bluish purple.  However, with colors of flowers, mutations to the enzymes in the pigment formation pathways can happen that would alter the color of the flowers.  i wouldn't be surprised to occasionally find pink and white blooms on any of the Delphinium species listed above.