Thx for response, is there any other way to understand if starter is ok, beside color?
The color change from medium brown to significantly lighter, and even creamy looking, indicates more yeast cells are in suspension.
There should also be a significantly larger amount of yeast precipitated on the bottom when not stirring/swirling, compared to where you began.
You can take a gravity reading of the starter beer after a few days using a hydrometer or refractometer.* If the result is lower gravity than from where you started, there was fermentation, IOW the yeast is not dead, but it still doesn't indicate how vital/viable she is, how many cells are alive.
You could do a cell count under a microscope. That's much, much more involved than observing color change in a starter or the forming of a thick yeast cake on the bottom of your starter vessel.
When the starter is done you could pitch the whole starter as is. Or cold crash in the fridge for a few days, then decant the mostly clear starter beer off the top leaving the thick slurry behind.
* When using a refractometer after fermentation has started, there will be alcohol present. You'll need to use a formula to correct the reading.
Refractometer Calculator - Sean Terrill