First, make sure that you're exporting with the latest version of in5 which currently is 3.8.7.
I did a test with in5 version 3.8.7, and white text is exporting as white with Text Rendering set to SVG.
So, I'm wondering if there could be either an issue with your file or how it's set up. If you save your document as an IDML file and save it as an INDD file, then that can fix minor corruption in the file.
If you're still having trouble with the SVG text after updating to 3.8.7 and starting from the IDML file, I'd be happy to take a look at your InDesign file or a sample file that recreates the issue and your html5_output. You can send it to us here: