Using the editing feature STACKABLES in SNAPSEED to change parts of an image from color to black/white or the reverse.
Make all your editing adjustments in SNAPSEED and when finished, scroll to FILTERS and choose BLACK WHITE. Your image is now black and white, not color!
Tap at the top of your screen where you see the layers with the curved arrow. Then tap on VIEW EDITS in the menu.
This will show you all the layers at the bottom right of your screen with Black&White highlighted in blue.
Tap on BLACK&WHITE to open up the three symbols to the left. Choose the middle box with what looks like a paintbrush. Tap on that symbol.
Decide if you want to work in color to reveal black/white or reverse the process using the INVERT symbol on the lower left; tap on that to switch the process.With your finger you can now paint back the color into specific areas of the photograph. You can pinch with your fingers to make it larger to be able to "stay in the lines." If you need to make adjustments to your "coloring" you click on the arrows in the middle to increase or decrease the effect.
You can turn on the mask of the layer to see what you have revealed or concealed.
When you finished with this edit you need to tap on the arrow at the top left of your screen to take you back to where you can save the entire project.
When you are finished, SAVE A COPY!
NOTE: You can use this STACKABLES edit in other tools and filters in SNAPSEED to reveal/conceal the layers underneath the open blue layer. Try it and see! You will be amazed!