Inventory Glitch

He is talking about the model screenshot that you would see on the website's marketplace. Another approach is to flood the surrounding area of a model with light boxes, so a list of steps to reproduce would be the following:

1. Spawn a new model - doesn't have to be fancy, can be just a block, but paint in light gray so the next step is more noticeable
2. Spawn several light boxes - change them to a color that is easily recognizable, like pink or cyan
3. Place these light boxes near and close enough to the model that is looks like it changes color
4. Add the model to your inventory
~~~ The model in your Inventory is going to look normal, but it isn't going to when you upload it ~~~
5. Select the model from your inventory, add a price, name and description and upload it your marketplace
6. Go to your profile page, click on "Marketplace"
7. Find your model
-> You'll see the model look like the color of the light box you used, even though its painted color is light gray. Like GodCreator said, you can also do this with Skyboxes, but it's not going to be as dramatic as you can do with light boxes.

EDIT: Here's an example of a slime box flooded with red light, which makes the appearance of a lava like texture - us.kogama.com/profile/22539/marketplace/model/72738/

Double edit: the model image itself, in case you don't want to go to the link -

Yay I was sorta helpful Thanks jatsu Xd