The slime mould plasmodium comes in a variety of colours and can shift according to substrate, pH, and other environmental factors. Yellow is the colour most commonly found as it is associated with some commonly occurring slime moulds such as Fuligo septica and Physarum polycephalum etc. White plasmodia are also fairly common. The plasmodium grows and enlarges hidden in the forest debris (rotting wood, lead mould etc) then at maturity goes through an active migration phase as it moves to a site for fruiting. In this case the plasmodium is engulfing a green plant. It is essentially an epiphyte at this stage and will do no harm to the plant. Within a day or so, it will transform into a spore containing fruitbody, dry up and blow away.