Can't set field color back to clear

Description

When a field's color is changed, it's not possible to set it back to clear:

Steps to reproduce

1. Change the color of the field using the properties dialog (double click)
2. The field gets its new color
3. Change the color of the field to clear
4. The field keeps its color

KiCad Version

Application: KiCad Schematic Editor x64 on x64

Version: (7.0.0-rc1-378-ge76fd128c3), release build

Libraries:
	wxWidgets 3.2.1
	FreeType 2.12.1
	HarfBuzz 5.0.1
	FontConfig 2.14.1
	libcurl/7.83.1-DEV Schannel zlib/1.2.13

Platform: Windows 10 (build 19044), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Jan 23 2023 06:17:37
	wxWidgets: 3.2.1 (wchar_t,wx containers)
	Boost: 1.80.0
	OCC: 7.6.2
	Curl: 7.83.1-DEV
	ngspice: 38
	Compiler: Visual C++ 1934 without C++ ABI

Build settings:
	KICAD_SPICE=ON