How do I make items that pass through a part have a particle emitter to the item?

I also need to know if you can change the color of the particle effect within the script

here is the script that I'm currently using for a mesh upgrader:

meshUpgrade = true

meshID = "http://www.roblox.com/asset?id=160003363"

textureID = "http://www.roblox.com/asset/?id=160003344"

script.Parent.Upgrader.Touched:connect (function(Part)

if Part:FindFirstChild("Cash") then

    Part.Cash.Value = Part.Cash.Value + 5

    if meshUpgrade == true then

        for i,v in pairs(Part:GetChildren())do
            if v:IsA("SpecialMesh") then
                v:remove()
            end
        end

        local m = Instance.new("SpecialMesh",Part)
        m.MeshId = meshID
        m.TextureId = textureID
    end
end

end)