Runner Bean Colour

Hi all. I've been harvesting my beans for growing next year and have discovered something I have not seen before. I have been growing White Lady and Crimson Emperor close together.  I have come across black or very deep purple beans. As per the picture they should be a pinky mottled and black colour. As you can see some are coming out pure black.
Do you think there has been some cross pollination here? Has it created a different strain?
Thanks all.

Crimson Emperor ? do you mean Scarlet Emperor?
SE usually have pinky /black mottled seeds, often all black or all purple - but if you are getting that colour seeds from White Lady plants then they have definitely been cross pollinated.

Hi yes, I meant Scarlet emperor. I think they came from the Scarlet Emperor plants, but not totally sure. Thanks.

I've been saving my own White Lady (white flowers, white seeds) seeds for years, and despite there being very few if any growers of runner beans in my area, at least two of the plants had red flowers this year, even though all the seeds sown were white. 

White Lady by name, but not pure in habits by the looks of it!   

Runner beans cross very readily with other runners.  They are pollinated by bees who travel quite some distance.
The Heritage Seed Library recommends a distance of 800m between different varieties if you want to maintain seed true to type.  Failing that, you need to put the beans in a net cage and trip pollinate them yourself or bag individual flowers after hand pollinating and then marking the fruit with string or similar as it grows.   A bit of a faff.
On the other hand you might be lucky, but you need to be prepared that next year's seed might not run true.
I belong to a couple of seed circles and I am a seed guardian for the HSL but I would never offer my runner bean seed to a seed circle or grow runners for the HSL as all around me grow runner beans and I don't have the time for the messing about I describe above.