What can I do when I see that water in the radiator is greyish

...first off, you're on the wrong side of the boulevard with "water"...we do not like water...because it reacts with things and makes "greyish" sludge...that blocks the t-stat...plugs the radiator vanes and makes it so your heater don't work no more~....correction....drain the grey....block flush....pullin out the freeze plugs and block drain plug...flushing all the smudge out of there and quickly replace freeze plugs drains...thermostat....WATERPUMP and any other components displaying this layer of grey matter...fill with 50/50 ethylene glycol/de-ionized water to the "full cold" markation on the translucent reservoir....and hope for NO overheats....~

some would buy a rad flush, run thru ,drain ,replace antifreeze with proper for that car, top with distilled water, hope your removing those shades when checking the colour, maybe its bright orange or green then let it be. although still check the freeze and boil point with a hydrometer