The tru Theme has a Grayscale Images option within the SPYR > tru Options panel. By simply toggling this option on you can automatically convert all of your images to grayscale.
If, however, you wish to selectively choose which images are color and which are grayscale you’ll simply need to add a class to your image.
With Grayscale Images Enabled
If you have Grayscale Images enabled and wish to display an image in color you’ll simply need to add a class of color to any images that you wish to be in color.
With Grayscale Images Disabled
If the Grayscale Images option is disabled you can add a class of bw to any image that you wish to be black and white.
How to add a class to your image
If you’re using the Text editor to write your Posts/Pages you’ll simply want to add the class to an image tag like so (in this example I’m adding the color class):
<img class="aligncenter size-full wp-image-462 color" alt="Image Title" src="http://example.com/image.jpg" width="960" height="960" />
Alternatively if you’re using the Visual editor you’ll simply want to click on the inserted image and then click on the Image Icon (it’ll appear along side a red circle which deletes the image). In the subsequent popup click on the Advanced Settings tab and enter color or bw into the CSS Class textbox and hit Update.
Workaround for Featured Images
The only images that you cannot manually add classes to are the Featured Images. This means that all Featured Images must either be set to Grayscale Images or left to be displayed as uploaded.
If you wish to have some Featured Images in grayscale and others in color you will need to disable Grayscale Images and convert individual images to grayscale prior to uploading. You can edit your images using a program such as Photoshop or a simple online tool such as Canva.