I wasn't keen on all that rainbow crap, so I threw this together based on the health pot particles.
Also, since (a) the point of the initial invincibility is to give you a chance to look about; (b) some rooms are too dark to look about when you first enter; and (c) laying any light sources negates said invincibility - I took care of that too!
Amend the JustEnteredChunkInvincibility section in AVWW\RuntimeData\Configuration\Particles.xml as follows:
<g pattern="JustEnteredChunkInvincibility">
<p name="Magic" y="64" stayrelative="true" offs="-15, 15, 0, 15"
sca="1.75, 2, 1, 1.5, 0.0001" anim="60" emiss="0.4" shad="InvisibleAffectsLighting"
ontrigger="1" />
<p name="Magic" y="64" stayrelative="true" offs="-12, 6, -22, 16" rot="180, 180, 0, 0"
sca="0.55, 0.7, 0.4, 0.5, 0.0001" anim="30" emiss="0.5" shad="AdditiveDouble"
fade="0.65, 0.75, 0.95, 0.8, 0.5, 0.75" ontrigger="1" />
<!--In case you want to revert to the old style:
<p name="Magic" y="64" stayrelative="true" offs="-32, 32, -10, 10" rot="180, 180, 0, 0"
sca="0.3, 0.6, 0.3, 0.6, 0.001" anim="40" emiss="0.4" shad="NormalAffectsLighting" perframe="1" />
-->
</g>
Extract the attached into AVWW\RuntimeData\Images\Particles\ and overwrite when prompted. (The originals are in a subfolder, if you want to go back.)
The attached screenshots don't really do it justice.