STEP 1:
Copy the image that attracted you and open it with photoshop("i like to call it PS").
STEP 2:
Select the Eyedropper-Tool(shortcut key: i) from tool box.[Note: this Eyedropper-Tool works same as that of MS Paint's Eyedropper-Tool. ]
STEP 3:
Click on the image and choose the color that you like using the eyedropper. The choosen color will be visible as foreground color.
STEP 4:
Now click on the foreground color and you can see Color-Picker-Window. On this window you can see the RBG and hexadecimal value[here #3B4FA8] of the color.