I recently got into a blender and a common issue I keep running into is having multiple colors on a model. I currently use blender 2.79 because I am more comfortable with this version. But when I export this model:
The colors do not show up in ROBLOX correctly. as seen below:
If anyone could help me with this it would be appreciated. I just need an easy way to get the texture map with color and be able to import it onto ROBLOX.
You can either bake the texture (which I personally do not know how to do), or seperate the mesh by material. To do this, go into edit mode and select the entire mesh. Then separate the mesh by material. I use 2.81, so I’m not sure how you would do this in 2.79, but I usually just right click and find the setting.
Edit: Then import each separate mesh. Make sure their origins are in the same place, though, so that the meshes’ location is the same in blender.
Solution—
Make them separate, what I mean by this is to delete the leaves from the original mesh in the Blender creation, and export the branches/trunk as a separate file for Roblox.
Then go back and press ctrl + z until your leafs come back to your creation. Then you will delete the branches and export the leaf mesh as a separate file. Then in Studio you can edit each mesh separately by having a brown color for the branches and wood texture. Etc for the leafs by putting grass and green on them.
Nice mesh by the way! 
Thank you, I was able to figure it out. Much appreciated. 
That helped a lot. Thanks for the feedback.
Your trying to colour a singular mesh and then bringing it over the Roblox.
Separately colour in the tree parts. e.g - Leaves , trunk, branches.
