How to blend colors using blend tools in Adobe Photoshop.

Click the Smudge tool from the toolbar. If you can't find it, click and hold the Blur tool to show its related tools, and then select the Smudge tool. You can also click Windows › Brushes and search for it in the Brushes panel.

Pick a brush tip and blend mode option in the options bar. 

Click Sample All Layers in the options bar to smudge using colors from all visible layers. To use colors from the active layer only, deselect that option.

Click Finger Painting in the options bar to smudge using the foreground color at the beginning of each stroke. Deselect Finger Painting to use the color under the pointer at the beginning of each stroke.

Click and drag over the area where you want to smudge the pixels.

If you don’t see it in the toolbar, click and hold the standard Brush tool to reveal the Mixer Brush.

To load paint into the reservoir, Alt-click (Windows) or Option-click (macOS) the canvas. The brush tip will reflect any color variation in the sampled area. For a brush tip of uniform color, select Load Solid Colors Only from the Current Brush Load pop-up menu in the Options bar. Another option is to simply select a foreground color.

Choose from the Brush Presets panel.

In the Options bar, select your preferences. Choose how much you want to load the brush with paint. Control how much paint the brush picks up from the canvas by increasing or decreasing paint wetness. You can also pick how much of the paint you’d like loaded in the reservoir, and how much you want your canvas paint to mix with your reservoir paint.

Drag the Brush in the image to paint, or draw a straight line by clicking a starting point in the image, holding down Shift, and clicking an ending point. You can also use the Brush as an airbrush by holding down the mouse button without dragging.