
For internet explorer you need somewhere create notepad file and paste this code:
/* Grey for market/menu background */
div#marketContainer,
div#bm,
div#allMarketsTreeContainer,
div#MVContentWrapper,
div#MVHeaderWrapper
{ background-color: rgb(220,220,220) !important ; }
/* Standard back colour for buttons and headings */
table#runnerTable tr.runner td.b1,
th.backHeader,
td.pressedBack div.buttonAppearance,
thead.back,
td#MVHeaderBackCell,
td.MVContentBack1stResting,
td.MVContentBack1stDepressed,
tr.MVHeaderBackBoldedHeader
{ background-color: rgb(140,140,250) !important ; }
/* Lighter back colour for bet manager bets */
tbody.back,
.BMBackBetBackground
{ background-color: rgb(180,180,250) !important ; }
/* Standard lay colour for buttons and headings */
table#runnerTable tr.runner td.l1,
th.layHeader,
td.pressedLay div.buttonAppearance,
thead.lay,
td#MVHeaderLayCell,
td.MVContentLay1stResting,
td.MVContentLay1stDepressed,
tr.MVHeaderLayBoldedHeader
{ background-color: rgb(128,200,128) !important ; }
/* Lighter lay colour for bet manager bets */
tbody.lay,
.BMLayBetBackground
{ background-color: rgb(170,230,170) !important ; }
Then in IE Tools>> Internet Options>> Accessibility>>tick Format document using my style sheet, and then browse to your new notepad file.
For mozilla browser first you'll need to install the Firefox add on, Stylish from:
https://addons.mozilla.org/en-US/firefox/addon/2108
then Tools>>add ons>>extensions>>options>>write and paste this code:

@-moz-document domain(betfair.com) {
div#marketContainer, div#bm, div#allMarketsTreeContainer
{ background-color: rgb(210,210,210) !important ; }
table#runnerTable tr.runner td.b1,
th.backHeader,
td.pressedBack div.buttonAppearance,
thead.back
{ background-color: rgb(140,140,250) !important ; }
tbody.back
{ background-color: rgb(180,180,250) !important ; }
table#runnerTable tr.runner td.l1,
th.layHeader,
td.pressedLay div.buttonAppearance,
thead.lay
{ background-color: rgb(128,200,128) !important ; }
tbody.lay
{ background-color: rgb(170,230,170) !important ; }
}
If you want change colors, write new RGB colors values.