Shortcut for colors Photoshop CC 2017?

You could do this by setting up a dedicated swatch and then making use of the library.

1) Open a simple swatch this is 'photo filter colors' and I chose this one as it doesn't have many colors.

2) Delete each color by holding 'alt' or 'opt' on a Mac and click each color in turn to delete it.

and you'll get this

3) Now define your custom colors. I'm using a picture here to get colors rather than doing it manually with specific values.

Select the eyedropper tool, 'I' on the keyboard. Click on a color in the image you want to add to the swatch then move your mouse over the swatches panel

At this point the icon turns into a bucket and a single click allows you to add the color to the swatch

All you need to do is name the color in the popup

4) The clever part is the color is also added to your color library automatically

5) You can quickly add many more colors to build the new swatch like below

6) If you want save the custom swatch

7) Now that might seem like a real rigmarole but took me less than a minute to do. The important thing is once your dedicated colors are in the library they allow you to select your foreground color with a single mouse click without going back to the swatch panel. It's a very convenient way of using specific colors and I suppose it is like having a kind of shortcut.

I suppose there is a way, but you could just put those three colors in the swatches panel and then just click on one of the colors to make it the foreground color in the Tools Panel.