MGCB editor fails with a parsing error in latest "develop"

Prerequisites

I have verified this issue is present in the develop branch
I have searched open and closed issues to ensure it has not already been reported.

MonoGame Version

3.8.1.617-develop

Which MonoGame platform are you using?

N/A

Operating System

Windows

Description

In the current develop state, the MGCB tool fails to load a .mgcb configuration due to a parsing error.

In the current 3.8.1 release, the following is supported/permitted

/processorParam:ColorKeyColor={R:0 G:0 B:0 A:0}

However, now only the following is supported:

/processorParam:ColorKeyColor=0,0,0,0

So something has changed which has broken the backwards compatibility

Steps to Reproduce

Create a new .mgcb content package using the release MGCB editor
Add an FBX file to the content
Save and close the MGCB editor
Check the file contents and update the following:
```
/processorParam:ColorKeyColor=0,0,0,0
```
To
```
/processorParam:ColorKeyColor={R:0 G:0 B:0 A:0}
```
(Which is a previous XNA supported format, and also supported by the Release version of 3.8.1)
Re-open the .mgcb file and confirm it is working
Close the .mgcb file and reopen using the latest Develop version of the MGCB editor (3.8.1.617-develop).
Observe the file can no longer be opened.

Minimal Example Repo

No response

Expected Behavior

The format

/processorParam:ColorKeyColor={R:0 G:0 B:0 A:0}

Should be supported for XNA backwards compatibility

Resulting Behavior

MGCB editor fails to load

Files

No response

Actually, in further testing, the 3.8 mgcb editor also fails with the following error:

System.ArgumentException: Could not convert from string({R:0 G:0 B:0 A:0}) to Color, expected format is 'r,g,b,a'
But the error does not occur when the content project is opened, only saved.

So this is more of an XNA regression issue.

Likely an easy fix. Color parsing happens here:

MonoGame/MonoGame.Framework.Content.Pipeline/Builder/Convertors/StringToColorConverter.cs

Line 38 in a6ef14b

if (value.GetType () == typeof (string)) {

If anyone wishes to take a look at fixing it.

Thanks for the added info @mrhelmut ! I made an attempt to fix it over in #8167 . I tested the Repro steps where I was able to see the error before and am not seeing it after through a few tests.

Via debug it was failing before and works after.
Before making the change I ran a full cake build and ran the Editor version there. It failed before, and then after adding the fix I re-did the cake build and it worked after running from the Artifacts release.
Lastly I created a separate solution where I replicated the problem with 3.8.1.303 and after the fix I mapped the dotnet-tools entry dotnet-mgcb-editor-windows to the local version and the problem was resolved.

Hope this takes care of it! Let me know if there are any questions or concerns.

Fix looks good, although if possible, can we also have unit tests testing the both patterns @JakeLegendXIII ?

Fix looks good, although if possible, can we also have unit tests testing the both patterns @JakeLegendXIII ?

Absolutely! UnitTests have been added to the PR.