Apparently the designer cannot create the window for the Form. I tried your code and it worked fine for me as is so I don't know what the problem is. However, this is not really how you're supposed to derive from Form. Here is the proper way:-
vbnet Code:
  1. Imports System.ComponentModel
  2.  
  3. 'Prevents the Forms designer from loading
  4. 'as this Form is a base class from which your
  5. 'application's Forms can inherit, it's not meant to be designed upon
  6. <ToolboxItem(False)> _
  7. Public Class BlackComponent
  8.     Inherits Component
  9. End Class
  10.  
  11. Public Class EditorFormBase
  12.     Inherits Form
  13.  
  14.     Private _color As Color = Color.FromArgb(32, 40, 56)
  15.     Private _font As Font = New Font("segoe ui", 8.5)
  16.     Private _formBorderStyle As Windows.Forms.FormBorderStyle = Windows.Forms.FormBorderStyle.None
  17.     Private _foreColor As Color = Color.FromArgb(128, 144, 160)
  18.  
  19.  
  20.     <Browsable(True), DefaultValue(GetType(Color), "32, 40, 56"), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)> _
  21.     Overrides Property BackColor As Color
  22.         Get
  23.             Return _color
  24.         End Get
  25.         Set(value As Color)
  26.             MyBase.BackColor = value
  27.         End Set
  28.     End Property
  29.  
  30.     <Browsable(True), DefaultValue(GetType(Color), "128, 144, 160"), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)> _
  31.     Overrides Property ForeColor As Color
  32.         Get
  33.             Return MyBase.ForeColor
  34.         End Get
  35.         Set(value As Color)
  36.             If Not MyBase.ForeColor = value Then
  37.                 MyBase.ForeColor = value
  38.                 Invalidate()
  39.             End If
  40.         End Set
  41.     End Property
  42.  
  43.     Sub New()
  44.  
  45.         ' Add any initialization after the InitializeComponent() call.
  46.         SetStyle(Windows.Forms.ControlStyles.OptimizedDoubleBuffer Or Windows.Forms.ControlStyles.SupportsTransparentBackColor Or Windows.Forms.ControlStyles.UserPaint, True)
  47.         DoubleBuffered = True
  48.  
  49.         BackColor = _color
  50.         ForeColor = _foreColor
  51.  
  52.         Font = _font
  53.         FormBorderStyle = _formBorderStyle
  54.     End Sub
  55.  
  56.  
  57.  
  58.  
  59.  
  60. End Class

I put the above in its own code file. When I need an editor form I simply inherit from EditorFormBase by changing the designer file for whatever Form I'm making.