Quick question on transparency

I have been following the useful HOWTO on writing text to canvas and then to texture which is very useful. And I like the transparency effect. But I have noted that when I try to change have different colours of text other than white and continually update the text with a timer it fails to display the different colours, only the white is displayed…

my test project is here

https://playcanvas.com/editor/scene/442013

How can you continually write text of different colours with a transparent background.