Custom Color Ramp shows only black upon reload, must add color to ramp then remove in order to function

[iamhowardtheduck]

**Kibana version: 7.6.1

**Elasticsearch version: 7.6.1

**Server OS version: Running on CentOS 7, Kibana accessed via Windows 10

**Browser version: Google Chrome 80.0.3987.132

**Browser OS version: Windows 10

**Original install method (e.g. download page, yum, from source, etc.): yum

**Describe the bug:
When opening a map with a customer color ramp, the colors shown are all black. A new custom color must be added, then removed in order for the color scheme to properly function.

Steps to reproduce:

1. Create a map with EMS boundaries, where the fill color are custom values
2. Save the map, open any other part of Kibana, then return to the map to see only black colors
3. Add in extra custom color, color scheme returns, then remove the extra color setting

Expected behavior:
Custom color ramp should appear as configured

Screenshots (if relevant):

Errors in browser console (if relevant):
None

Provide logs and/or server output (if relevant):

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)

[nreese]

closed by #59953. Fix will be in 7.6.2 patch release.