Your texture could not be loaded, so it is displayed as a white box. The white box is tinted yellow because of
nameplate.monsterDiff:SetColor(240,100,0,1)
The texure could not be loaded because iconCFG.defaultboss[normal] returns nil in your code.
Lua Code:
defaultboss = {
normal = Myaddon.name .. '/textures/bossicon1.dds',
}
This lua code means the table defaultboss has a field called normal, which contains the path to the texture. However, when calling
defaultboss[normal] lua will interpret
normal as a variable and not the name of the field.
You need to call
iconCFG.defaultboss.normal or
iconCFG.defaultboss["normal"]