In Photoshop:

• Create a new document
• Create a shape
• Go to FX

• Gradient Overlay

• Click the the current gradient

• Create a new gradient

• Add color to the gradient path and you might want to use the color picker to find the colors

• Change the style to linear

Play around with the colors:

If it’s a Gradient Fill layer, when that layer is selected it should be possible to adjust its properties using the Properties panel, as you see in the picture below. In this way you don’t have to open a stack of dialog boxes; that’s why they recently made this improvement to make the options of more layer types immediately accessible in the Properties panel. In the picture below, you can see that I added a middle opacity stop set to 0% opacity. ·   · One thing that can confuse people is that the option they want, such as Opacity Controls, might be available in the Properties panel, but not visible. When this happens, make sure the options group you want is both scrolled into view (in case it’s hidden further down), and if necessary, also expanded (if it’s collapsed). · That’s the reason my screen shot is so tall. If it was shorter, Opacity Options would have been covered by the Layers panel unless I scrolled the Properties panel to bring the Opacity Options into view. · If the gradient was applied another way, it might be different. For example, you’d edit a Gradient Overlay effect in the Layer Style dialog box.

@alisonnnnn your link to the Gradients article works for me.  Here is what it says: You can define your own gradients in the Gradient Editor dialog box. A gradient can include two or more colors, or one or more colors that fade to transparency. Gradient Editor dialog box.A. Color Stop B. Color Midpoint C. Opacity Stop To define a gradient, you add a color stop to add a color to the gradient, drag the color stop and the midpoint icon to define the range between two colors, and adjust the Opacity stops to specify the transparency that you want in the gradient.From the Draw section in the toolbox, select the Gradient tool.To display the Gradient Editor dialog box, click the Edit button below the gradient sample.In the Preset section of the Gradient Editor dialog box, select a gradient on which to base your new gradient.To choose colors for your gradient, double-click the color stop, or click the Color swatch to display the Color Picker. Choose a color, and click OK.To adjust the color stop location of a color, drag the stop left or right.To add a color to the gradient, click below the gradient bar to define another color stop.To adjust the location of the transition midpoint between colors, drag the diamond below the gradient bar to the left or right.To delete the color stop you are editing, click Delete.To set the color transition’s smoothness, enter a percentage in the Smoothness text box, or drag the slider.If desired, set transparency values for the gradient by dragging the Opacity stops.To save the gradient in the gradient presets, enter a name for the new gradient, and then click Add to preset.Click OK. The newly created gradient is selected and ready to use.

You can take a look at a mesh gradient in Photoshop but Illustrator makes this insanely easy with a freeform gradient—which works exactly as you described. You click a gradient point and select a color. Illustrator Freeform Gradient

Define what you mean by "color". You can make a "one color gradient" by dragging the same color to both ends of the gradient ramp. This will, though, result in exactly the same result as a solid fill. If by "color" you mean hue and want a dark/black through "color" to light/white gradient then simply create a 3 color gradient with black at one end, your chosen color in the middle and white at the other.

You can just create a gradient-filled shape layer, then apply a Gradient Overlay Layer Style to that shape.

The Shape layer contains a gradient of 2 colors... then the Layer Style adds the third color.

Right-click/Control-Click the image above and choose Open image in new tab/window to see it larger if needed.