Can you use color splash on a photo that was edited in black and white or do you have to mask the photo before editing it in black and white?

Question

can you use color splash on a photo that was edited in black and white or do you have to mask the photo before editing it in black and white?

Answer 1

I think you are asking whether it makes an difference whether you create the mask before or after you edit the black & white version. The answer is that since the color version and the b&w version are on different layers (as seen here), it makes no difference when you edit the b&w version.
Also consider another technique that separates the color element in the image. Here, the area surrounding the color image is a line interpretation of the scene, similar to a Tone Line Conversion, a technique that was created with film many years ago.  (I am so old,  I still remember how it was done.) This is how to get the result similar to the one shown above but with a line illustration created in Photoshop replacing the b&w layer version:
1. Open an image. This technique is more successful if the image you select has many clearly defined edges.
2. Make a duplicate layer. (Cmd+J). It becomes Layer 1
3. With Layer 1 chosen, go to Filter>Blur>Smart Blur. Set the Quality to High and the Mode to Edge Only. The default settings are Radius 3.0, Threshold 25.0. To increase the amount of detail in the line conversion, raise the Radius setting. Use the white-on-black illustration within Smart Blur as a guide. Then click OK.
4. The line illustration will appear as white lines in a black background. To change this to black-on-white, choose Image>Adjustments>Invert.
5. Insert a new layer below Layer 1. It will serve as the background for the line illustration. To do this, hold down the Command key while clicking on the New Layer symbol at the bottom of the Layers panel. It is the second symbol from the right. It will become Layer 2.
6. Fill this new layer with a light color. To do this, click on the Foreground Color symbol in the Tools section. It will open the Color Picker. Choose a light color and click OK.
7. Choose Edit>Fill. Use: Foreground Color.  Mode: Normal. Opacity: 100% and click OK. Layer 2 will fill with the color. Although it will not appear in the image because Layer 1 is above it, a quick check of the Layers panel will confirm that the color you chose has filled Layer 2.
8. Remove the white area from in Layer 1. Go to Layer 1. Choose the Magic Wand tool. Uncheck the Contiguous box in the Options Bar and click in a white area of the image. Next, click the Delete key.  Choose Select>Deselect to remove the marching ants. 
9. (Optional)  You may now change the line illustration in Layer 1 from black to a dark color compatible with the color in Layer 2. To choose the color, click on the Foreground Color symbol in the Tools section. It will open the Color Picker. Choose a suitable dark color and click OK. While in Layer 1, click the first symbol next to the word  Lock:  in the Layers panel above Layer 1. This will prevent the dark color from appearing in the blank area of Layer 1. Choose Edit>Fill. Use: Foreground Color.  Mode: Normal. Opacity: 100% and click OK. The black lines will change to the dark color you chose.
10. Combine Layers1 and 2: While in Layer 1, choose Layer>Merge Down. The layers are combined into a single layer called Layer 2.
11.  Add a black mask to Layer 2 by clicking on the Mask symbol at the bottom of the Layers panel. It is the symbol to the right of the fx symbol. Where you would like full color objects to appear within the line rendition, paint in white on the black mask with a brush set to either soft-edge or hard-edge as the illustration and your taste dictate.