I am shooting digital so I have used photoshop to convert my image to black and white and then used filters to show how each affects the final shade of grey.
I found four balloons in each of the colours we are studying. I took the photo after using a grey card to determine what my exposure would be.
The first image below is that of the coloured balloons.
Now using photoshop, Image>adjustments>black and white, the image is now converted. This is the result leaving at the default settings.
Default Grey Scale
The next image is the result when applying just the red filter. What happens is where the colour is red this comes through brighter. Colours without red such as the blue and the green are filtered out so become darker. My yellow balloon is affected by the red filter so has also converted to a lighter tone.Red Filter
Now using just the yellow filter The yellow balloon is bright, the blue and green balloons are not quite as dark as when just using the red filter.
The green filter lets the green colour come through but blocks the red. The red and green balloons now are quite similar in tone.
The affect of the blue filter is very dramatic. Letting blue light in while blocking the other colours, gives my blue balloon the appearance of almost being white.Blue Filter
In my version of photoshop under the black and white converter I have used, I have additional filters of cyan and magenta.
For my final image I have adjusted the filters to control the amount of light for each colour thereby giving me tones in my black and white image that make the image more interesting. Although this is a simple image with a subject matter that is not particularly interesting, it none the less demonstrates just how colour creates tone in black and white.
For this image the red filter affected both the red and the yellow balloons (this will be because of the shade of yellow the balloon is) however when I adjusted the magenta slider I was able to change the tone of the red balloon without affecting the yellow balloon.
These subtle differences can make a huge difference when converting images of people. Adjusting the tone of lips, eyes, freckles for example without changing the entire skin tone.
This final image is one from another project I am working on. I have spent time converting to black and white then adding back a little colour. Adjusting various parts of the image to get the tones that I wanted for the image. I have included this to show my understanding of how removing or adding colour to an image affects the final tone.