EF Core Unable to determine the relationship represented by navigation property 'Colour.ColourGroups' of type 'ICollection<ColourGroup>' - entity-framework-core

Question

I have the following 3 tables in a legacy database.
CREATE TABLE Colour(
ColourCode char(3) NOT NULL,
CONSTRAINT PK_Colour PRIMARY KEY CLUSTERED
(
ColourCode ASC
)
CREATE TABLE ColourGroup(
ColourGroup varchar(6) NOT NULL,
CONSTRAINT PK_ColourGroup PRIMARY KEY CLUSTERED
(
ColourGroup ASC
)
CREATE TABLE Colour_ColourGroup(
ColourCode char(3) NOT NULL,
ColourGroup varchar(6) NOT NULL,
CONSTRAINT PK_Colour_ColourGroup PRIMARY KEY CLUSTERED
(
ColourCode ASC,
ColourGroup ASC
)
ALTER TABLE Colour_ColourGroup WITH CHECK ADD CONSTRAINT FK_Colour_ColourGroup_Colour FOREIGN KEY(ColourCode)
REFERENCES Colour (ColourCode)
ALTER TABLE Colour_ColourGroup WITH CHECK ADD CONSTRAINT FK_Colour_ColourGroup_ColourGroup FOREIGN KEY(ColourGroup)
REFERENCES ColourGroup (ColourGroup)
and the following EF classes to represent them in code
public class Colour
{
public string ColourId { get; set; }
public ICollection<ColourGroup> ColourGroups { get; set; }
}
public class ColourGroup
{
public string ColourGroupId { get; set; }
public ICollection<Colour> Colours { get; set; }
}
public class ColourColourGroup
{
public string ColourId { get; set; }
public string ColourGroupId { get; set; }
public Colour Colour { get; set; }
public ColourGroup ColourGroup { get; set; }
}
I'm using Fluent API to link ColourColourGroup to the Colour_ColourGroup table and to specify some DB column names.
builder.Entity<Colour>(entity =>
{
entity.Property(e => e.ColourId).HasColumnType("char(3)")
.HasColumnName("ColourCode");
entity.Property(e => e.FinishId).HasMaxLength(3);
entity.Property(e => e.Description).HasMaxLength(30);
entity.HasKey(e => e.ColourId);
});
builder.Entity<ColourGroup>(entity =>
{
entity.Property(e => e.ColourGroupId).HasMaxLength(6)
.HasColumnName("ColourGroup");
entity.HasKey(e => e.ColourGroupId);
});
builder.Entity<ColourColourGroup>(entity =>
{
entity.ToTable("Colour_ColourGroup");
entity.Property(e => e.ColourGroupId).HasMaxLength(6)
.HasColumnName("ColourGroup");
entity.Property(e => e.ColourId).HasMaxLength(3)
.HasColumnName("ColourCode");
entity.HasKey(e => new { e.ColourId, e.ColourGroupId });
});
But I don't know how to link the 3 tables together. If it was just a one-to-many relationship between Colour and ColourGroup, I think you'd use InverseProperty (or whatever the Fluent equivalent is) on ColourGroup.Colours.
Any query that accesses these entities fail with the above error, for example:
var group = _context.ColourGroups.Where(g => g.ColourGroupId == "ALLPC").FirstOrDefault();
How do I tell EF that the Colour.ColourGroups and ColourGroup.Colours properties are "mapped" by the corresponding properties in ColourColourGroup?