@J-G:
I have implemented custom color for negative values in every jujiboutils numeric component DB aware and non DB aware (integer, float and currency). Mask for negative value format was already working. You can download latest code from lazarus-ccr SVN
In your case, set DisplayFormat to: #,0.00€;(#,0.00)€ and NegativeColor to cl_red to get the desired result.
I suggest you to use currency components to deal with currency values instead of float one.