WoWInterface - need help about debuff desaturated

I use these code to make debuff (not casted by me) desaturated, but sometimes some buff desaturated too, any idea?

Lua Code:

local PostUpdateIcon = function(_, unit, icon, index, _, filter)
    local _, _, _, _, dtype = UnitAura(unit, index, icon.filter)
    local texture = icon.icon
 
    if icon.isDebuff and dtype and UnitIsFriend("player", unit) then
        local color = DebuffTypeColor[dtype]
        icon.bg:SetVertexColor(color.r, color.g, color.b)
    else
        icon.bg:SetVertexColor(0, 0, 0)
    end
 
    if icon.isDebuff and not icon.isPlayer then
        texture:SetDesaturated(true)
    else
        texture:SetDesaturated(false)
    end
end