Field Y Could be defined as a calculation field, but using a different TABLE (not just another layout) as you describe adds a great deal of flexibility to your system. The back ground colors could also be achieved with a conditional format using the same casefunction approach, but it also has the same limitations.
So using that second table, set up this relationship:
FieldXTable::FieldX = FieldYTable::FieldX
See the first post of: Common Forum Relationship and Field Notations Explained if this notation is new to you.
In the FieldYTable, define three fields: FieldX, FieldY, ColorFIeld--> make this last field a field of type container.
On your Layout based on the FieldYTable, create records for each value of FIeld X, and enter the text that you have shown in your first post here. Then, Enter layout mode and use the rectangle tool to create an orange rectangle on your layout. Copy it to the clipboard. Return to browse mode and paste the copied rectangle into the Color field. Repeat for each of the other colors.
Now go to your layout based on FIeldXTable. Format FieldXTable::FieldX with a value list of values from FieldYTable::FieldX. Put the Field Y and ColorField fields from the FieldYTable on this layout. In data formatting on the inspector, select the "Reduce or enlarge" option and clear the "maintain proportions" check box so that the pasted rectangle resizes to fully fill the container field.
Note: You don't have to use FileMaker in layout mode to create the color rectangles. Any simple graphics program, such as Windows Paint can be used to create these rectangles so that you can copy and paste them into the colorFIeld containers.
Perfect, thank you so much!