Find alternative color for springNode on Stretch Screen

[arouinfar]

On the Stretch Screen, the springNode is damped. The other screens have zero damping, so to cue that the Stretch Screen is different, the springNode was given a color.

While the purple springNode has good contrast against the other colors in the sim, it is not distinguishable from the gray springNode for those with Protanopia.

Self-assigning to find an alternative color.

https://github.com/phetsims/masses-and-springs-basics/blob/master/js/stretch/view/StretchScreenView.js#L93

[arouinfar]

I tested two other purple options, and both had improved contrast against the gray springNode. Option 2 has just a bit more contrast, so I'd like to go with that @Denz1994.

1

frontColor: new Color('rgb( 197, 112, 162 )'),
middleColor: new Color('rgb( 159, 16, 100 )'),
backColor: new Color('rgb( 79, 8, 50 )')

2

frontColor: new Color('rgb( 162, 106, 172 )'),
middleColor: new Color('rgb( 100, 6, 117 )'),
backColor: new Color('rgb( 50, 3, 58 )')

[Denz1994]

Color selection 2 was applied to the springs on the Stretch screen. Thoughts @arouinfar?

[arouinfar]

Looks good! Thanks @Denz1994.