Little bit of a problem...

Please tell me if this is the wrong place to post this, but, whenever I render my model, it always changes the colours. I was wondering if anyone could help me!
What it should look like:

What the rendered preview looks like:

What the materials of an object look like when previewed in Object Mode is not a good indicator of what they will actually look like when rendered.

What does the material look like in the material preview window?

Haven’t you by accident clicked one of VCol Light / VCol Paint buttons in Material tab of Material context buttons? Uncheck both. This will work, if you painted it with vertex colors also. If you used texture, add another on top.