Is there a photographer's tool that wil sample the actual RGB color of an item?

Of course, you can snap a photo and then scan it and use an eyedropper tool in Photoshop to sample. But if you shoot a photo of a wall, the lighting varies across it, especially if you must use a single flash to light it. Even if you use a set of photo-floods and bounce the light, the color temperature of the lighting comes into play. Is there a tool that you can hold up to a wall or backboard or such and sample the exact RGB color in natural filtered sunlight? If so, what’s it called, and who might I suggest would have one?

I have a Website client who is absolutely obsessing about matching the color of a burlap mounting board she has in her shop. I showed her a great online tool called the Color Scheme Designer and showed her how to use it. The Green in her logo is #554422 hex (40, 92, 60 HSL). But she just can’t seem to arrive at a color she thinks is “right” for the burlap or kraft paper color to go with her logo green. Even though the various complimentary light browns on the color wheel look great with her green, it’s not the same as the burlap wallboard in her shop. Any suggestions of how we could get the exact color of that burlap would be appreciated.