Use filters to make colourful sketches
Open your image and press Cmd/Ctrl+J to duplicate the layer. Press Cmd/Ctrl+Shift+U to quickly desaturate it. Drop the layer Opacity to 50%.
Press Cmd/Ctrl+J to duplicate. Bring back Opacity to 100%. Press Cmd/Ctrl+I to invert. Set blend mode to Color Dodge. Go to Filter>Blur Gaussian Blur. Use 30px, click OK.
Press Cmd/Ctrl+I, blend mode to Multiply. Add a layer mask. Select the Brush tool. With a soft brush, paint black in the mask to reduce the effect in areas.