[Fizzlemizz]

Again, the same as Kanegasi but slightly different in order to bake the border colouring into your created frames:

local function ColorBorders(self, r, g, b, a)
    for i=1, 4 do
        self.borders[i]:SetColorTexture(r, g, b, a and a or 1)
    end     
end
 
local function CreateBorderFrame(name, thickness)
    local f = CreateFrame("Frame", name)
    f:SetSize(40, 40)
    f.bg = f:CreateTexture()
    f.bg:SetAllPoints()
    f.bg:SetTexture("Interface/BUTTONS/WHITE8X8")
    f.bg:SetVertexColor(0, 0, 0)
    f:SetResizable(true)
    f:EnableMouse(true)
    f:RegisterForDrag("LeftButton")
    f:SetScript("OnDragStart", function(self)
        self:StartSizing("BOTTOMRIGHT")
    end)
    f:SetScript("OnDragStop", function(self)
        self:StopMovingOrSizing()
    end)
    f.SetBorderColor = ColorBorders
    f.borders = {}
    local offset = (thickness/2)
    for i=1, 4 do
        f.borders[i] = f:CreateLine(nil, "BACKGROUND", nil, 0)
        local l = f.borders[i]
        l:SetThickness(thickness)
        l:SetColorTexture(1, 1, 0, 1)
        if i==1 then
            l:SetStartPoint("TOPLEFT", -offset, 0)
            l:SetEndPoint("TOPRIGHT", offset, 0)
        elseif i==2 then
            l:SetStartPoint("TOPRIGHT", 0, offset)
            l:SetEndPoint("BOTTOMRIGHT", 0, -offset)
        elseif i==3 then
            l:SetStartPoint("BOTTOMRIGHT", offset, 0)
            l:SetEndPoint("BOTTOMLEFT", -offset, 0)
        else
            l:SetStartPoint("BOTTOMLEFT", 0, -offset)
            l:SetEndPoint("TOPLEFT", 0, offset)
        end
    end
    return f
end
 
local f = CreateBorderFrame("ZaxFrame1", 1)
f:SetPoint("RIGHT", UIParent, "CENTER", -20, 0)
f = CreateBorderFrame("ZaxFrame2", 18)
f:SetPoint("LEFT", UIParent, "CENTER", 20, 0)
ZaxFrame2:SetBorderColor(0.2, 0.5, 0.8)