Highlights We present the production of an electrochromic screen-printable paste based on Prussian Blue. These blue electrodes display excellent spectroelectrochemical reversibility and high catalytic activity towards the reduction of H2O2.  These blue electrodes enable both the electrochemical and optical quantitative determination of hydrogen peroxide.  The reported blue electrodes are highly suitable transducers for the construction of oxidase-based biosensors.  A glucose biosensor is presented to demonstrate the spectroelectrochemical capabilities of these new electrodes. AbstractPrussian Blue (PB)-modified graphite screen-printed electrodes are increasingly being used in electrochemical biosensors. However, they do not allow the observation of the electrochromism of PB. This work presents the construction of PB-based, electrochromic screen-printed biosensors. Although electrically more resistive than their graphite counterparts, these new PBbased electrodes enable both the amperometric and colorimetric detection of hydrogen peroxide.This is the first time that this has been achieved using screen-printed electrodes, and we demonstrate it spectroelectrochemically on a glucose biosensor. The biosensor electrochemical performance equals that of previously reported PB/graphite electrodes, being able to detect down to 4 µM H2O2 and 54 µM glucose. At the same time, and in contrast to PB/graphite electrodes, the new PB-based electrodes afford the optical detection of these two analytes down to 1.2 µM and 15 µM, respectively. The dynamic ranges of the glucose biosensors obtained at the PBbased electrodes are 0.1-1 mM (amperometric) and 0.025-2.5 mM (Colorimetric), matching the physiological glucose concentration range in body fluids other than blood or serum.