Contours and how to create them using Photoshop gradients tutorial
A quick way to create gradients via a shape (of course, you can create gradient contours in other ways) is to add a style with a gradient
1) custom shape tool or ellipse etc
2) shape option
3) apply shape design as a shape layer
4) layer menu
5) layer style
6) outer glow style
7) click the gradient option button if it is not already selected, not the solid color and set the blend mode to normal and opacity 100% and technique precise and spread 0 and size 250
Once you are on the layer styles panel and the outer glow
1) you will see a gradient dropdown
2) click that to display the gradient editor
3) go to the bar in the center of the panel and click the bottom of the gradient line to add a stop
4) change the color via the color setting on that panel.
5) Click in different positions along the gradient line to add more stops to the line.
If you want a more even contour with the gradient then go along the line perhaps clicking at 0% and 10% and 20% etc and set the color from green to black and green to black and so on alternating the colors.
You can make any number of contour variations by simply setting the positions to 0% 5% 10% 20% 50% etc as well as changing the color alternating, perhaps use two blacks to one color combinations etc (up to you).
6) Once you have that contour gradient you can then either click OK to add the result to the outer glow panel as well as click the new button to add it to the gradients list.
You now have your contour start point for the gradient and the selected shape.
It should be noted that you don't have to perform the above in the outer glow panel, the generation of the contour gradient can be done while selecting the gradient overlay, gradient fill etc as well and then added to the list for future use. Once you have the contour gradient shape then you can also just flatten the image and then use various adjustments or effects to modify it such as hue and saturation on the left or the camera raw filter on the right
You may like to create a large selection of similar presets and save them as a new GRD file for future use. It is a pity that there are no additional controls to modify the color of the preset as well as saturation etc for the controls (you could do this in a variety of plugins such as the KPT ones).
You can find many contour themed gradients via the 32,000 Photoshop and elements gradients collection from this site
You can find additional contour themed resources for Photoshop and others on the site such as contour / offset fonts and eps vector shapes as well as a set for use in Photoshop and elements only such as contour / offset custom shapes and a set of stroke designs (that can also be used as a great set of patterns and not just brush strokes) such as contour / offset brushes for Photoshop, psp, Indesign, Affinity Photo etc
You can create a contour by using a gradient style preset made of multiple gradients stops (as described above) and add an outer glow style to any selected shape etc via layer effects / styles dialog in the layers menu. Change the color of the outer glow from solid color to the gradient. You can change the outer glow style technique to precise and set the opacity and blend mode (such as normal) and spread and size as required.
You can stop at this point if you want a colourful contour for the shape but if you want a black and white contour or perhaps different colors, rasterize the layer effect via the layer menu rasterize layer effects command.
You can then go to the
1) image menu
3) threshold to reduce the image to black and white contours.
Left is a single ellipse with a single outer glow and rasterized and then threshold adjustment added
You have the original layer with the glow all rasterized and remaining as a layer and then a new outer glow is added to the artwork using the same preset. It is a pity that the outer glow as well as all the other features in the layer menu cannot have a multiple / copies / repeat feature (many apps do but PS for some reason does not). Note that the circles are a little cruder. This is not so notable if you use a more unusual vector path than a basic ellipse
A quick way of create ever more contours with the shape is to use the layer menu and smart objects and convert to smart object and add the same outer glow to that. You can then turn that into a smart object and add the same outer glow to that to create 10s of rings to the design.
Personally, I wish Photoshop would add a repeat gradient x 10 feature where the gradient repeats itself and mirrors etc (some applications have that feature)
Of course, with just a circle you really don't need the shape in the first place. Just go to the gradient tool and then add more stops. You can stretch out the gradient panel to fill most of the screen to give more space for more stops.
I am certain there is a limit on the stops, never found one as yet.
The easiest way to add the stops is to add lots of them in the same color and then click in between those stops with another color such as white and do that for all the other stop gaps. You can then move them to 1% 2% etc positions as required afterwards
1) gradient tool
2) select the gradient panel
3) go to the gradient stops
4) add more stops
5) click ok
You can find many tutorials on the site such as how to use the Adobe generator feature in Photoshop and how to use the Photoshop gradients with transparency tutorial and how to use the Photoshop gradients with text / type and how to use the new Photoshop search feature in CC 2017 for quick access to all the commands and stock photos