Candlestick Color for Open Equals Close, or for Hollow Candles when Previous Close equals Today's close

Is there a "standard" convention for setting the color a Candlestick when the Open and Close are equal?

It appears to me that most (of the few charting systems I have looked at) are using:

UP-color   if Close > Open
DOWN-color if Close <= Open

Thus the DOWN-color is used when they are equal.

I did find one charting system that used a third color (Gray) to indicate when the Open and Close are equal.

I am trying to find out if there is any kind of convention, or consensus, for this, or if the choice of Open==Close color varies very much from system to system.

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A similar question is how to handle the first candle on a Hollow-and-Filled Candlestick chart:

As you know, in Hollow-and-Filled candlestick charts, the color is not based on Close versus Open, but rather on Close versus Previous Close. But the first candle does not have a Previous Close.
Is there a convention for the color of the first candle on such a chart?