revisit "color" and "paint"

[pixelzoom]

This issue caused my to pause and bail while working on phetsims/bamboo#16.

There are a bunch of related "color" issues, most of which are bogged down by the topic of this issue:

#1115,
#948,
phetsims/axon#221,
phetsims/joist#681
...

We have a confusing number of things that are considered "color" or "paint". The ones that I know about are:

null
CSS string
Color
ColorIO
Property(...) // roll your own
ColorProperty
PaintColorProperty
ColorDef
ColorDefIO
PaintDef

... with ColorValue, ColorValueIO, ColorValueProperty recently proposed in #1115 (comment).

And:

• some promote null to "transparent", other fails with null
• some have IO types, some don't
• nothing supports the test for value == null | value instanceof Color | ( typeof value === 'string' && Color.isCSSColorString( value ), some variation of it is duplicated many times

In light of scenery and PhET-iO changes, someone needs to revisit "color" (and perhaps "paint") and come up with a plan for revising and cleaning this up.

Assigning to @ariel-phet to prioritize and assign.

[ariel-phet]

Labelling as high priority for at least an initial discussion at iO meeting

[zepumph]

We brought this up in phet-io meeting today. It was suggested that things may get easier if we stop supporting string in ColorDef and to always use Color. @kathy-phet added this to common code rocks in the quarterly planning doc. Assigning to dev meeting for further discussion after priority is decided on.

[zepumph]

It was also mentioned that likely we will want a sub team to tackle this.

[zepumph]

• colors.html and Studio need a color editor that supports alpha joist#681 also.

[mattpen]

Removed high priority in discussion at dev meeting

[samreid]

Developer Meeting:

We noticed that this is not scheduled as a quarterly goal for Q1 2021. When it becomes a quarterly goal, we will add it back to developer meeting to create a subteam to proceed.

[pixelzoom]

As noted in Slack today... It seems like this issue has gotten a tad worse since converting to TypeScript. None of the types listed in #1135 (comment) have gone away. And we've added

• IColor
• IPaint
• PaintColorProperty

... and may be others that I'm not aware of.

Also as noted in Slack by @marlitas, there's currently no support for converting an IColor to a Color. That makes life difficult when you have a parameter or option of type IColor, and you need to apply some Color function, like colorUtilsBrighter.

[samreid]

2708621 makes Color.toColor accept an IColor argument.