"I ain't talkin' to no law!" she said to the sheriff just as she looked at the black and white photograph he had given her. "And I ain't never stolen no ruby!"
"These photos are not coloured, ma'am," the sheriff stroked his moustache with one hand. The other he placed on his holster. "I never said what colour the gem was."
"Yeah, you did," she responded, but the sheriff stayed silent and slowly reached for his handcuffs. "Wait," she stepped back, nearly tripped over a rock. "Ya know how them colourblind are? Well, I am colour far-sighted. I can see what them colours are even in black and white photos."
The sheriff winced as he shook his head. "You're under arrest."