Impurity dots turn yellow in screenshot

[KatieWoe]

Test device:
Dell Laptop
Operating System:
Windows 10
Browser:
Chrome and Firefox
Problem description:
For phetsims/qa/issues/179
When a screenshot is taken using the PhET menu the impurity dots appear to be the color of the background (i.e. yellow). They should be black dots.
Steps to reproduce:

1. Adjust the sliders so that a fair number of impurity dots are visible.
2. Go to the PhET menu
3. Select "Screenshot"
4. Open and view the resulting image.

Screenshots:

Troubleshooting information (do not edit):

Name: ‪Resistance in a Wire‬
URL: https://phet-dev.colorado.edu/html/resistance-in-a-wire/1.5.0-rc.8/phet/resistance-in-a-wire_all_phet.html
Version: 1.5.0-rc.8 2018-08-23 22:07:53 UTC
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36
Language: en-US
Window: 1536x737
Pixel Ratio: 2.5/1
WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium)
GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 30 uniform: 4096
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 16384x16384
OES_texture_float: true
Dependencies JSON: {"assert":{"sha":"928741cf","branch":"HEAD"},"axon":{"sha":"cc053b4d","branch":"HEAD"},"brand":{"sha":"89d28f63","branch":"HEAD"},"chipper":{"sha":"fe3cb370","branch":"HEAD"},"dot":{"sha":"56c1d4b8","branch":"HEAD"},"joist":{"sha":"f047fb1b","branch":"HEAD"},"kite":{"sha":"b6071478","branch":"HEAD"},"phet-core":{"sha":"f35ff65e","branch":"HEAD"},"phet-io":{"sha":"d54be499","branch":"HEAD"},"phet-io-website":{"sha":"28284828","branch":"HEAD"},"phet-io-wrapper-classroom-activity":{"sha":"c84e3046","branch":"HEAD"},"phet-io-wrapper-lab-book":{"sha":"ebf7c7dc","branch":"HEAD"},"phet-io-wrappers":{"sha":"ce57c3e2","branch":"HEAD"},"phetcommon":{"sha":"a5a7478c","branch":"HEAD"},"query-string-machine":{"sha":"485e174e","branch":"HEAD"},"resistance-in-a-wire":{"sha":"b70a62da","branch":"HEAD"},"scenery":{"sha":"33290b5e","branch":"HEAD"},"scenery-phet":{"sha":"42b0cff2","branch":"HEAD"},"sherpa":{"sha":"9c6ec322","branch":"HEAD"},"sun":{"sha":"2e7beb55","branch":"HEAD"},"tandem":{"sha":"7f499d9e","branch":"HEAD"}}

[jessegreenberg]

Almost certainly caused by #165 changes, assigning to me. I am not seeing this in other sims that use CanvasNode.

[jessegreenberg]

If I add context.fillStyle = 'black' somewhere above context.fill() in paintCanvas the problem goes away. fillStyle is supposed to have a default of black, not sure why it isnt showing up in the screenshot feature.

[jessegreenberg]

This is fixed in master, marking with a label so this makes it into the release branch.

[KatieWoe]

Looks good on master

[zepumph]

We will not be pulling this into the 1.5 rc. If this has been confirmed fixed in master it can be closed.